Maps and map interpretation

DETERMINE DIRECTIONSAND AREA

DISTANCE AND SIZE AREA MEASUREMENTS

Topographical maps can be potentially used to asses the measurements of the geographical features observed with reflection to the respective actual areas represented. It is therefore important to learn how the measurements of the geographical features of represented areas can be established from the topographical maps.

The popular ground measurements which can be established from the topographical maps are of distance and size of different land structure.

DISTANCE DETERMINATION

Distance is defined as the length of an elongated object or space between the two points on the

earth’s surface expressed in units of linear measurements like; meters, feet, kilometers and miles.

Distance measurements of any elongated object on the topographical map has to take into consideration of the following key issues.

· Map scale; The ratio of distance between the map and the actual ground represented. This enables the change of convention distance (CD) into actual ground distance.

· The appearance of the elongated object on the topographical map given whose distance is to be measured. This determines the technique to be applied to get the CD.

Distance determination

For straight elongated objects.

For straight elongated objects, one has to use a ruler more directly to get the conventional distance of the object on the map. i.e. a ruler has to be placed along the elongated object to be measured.

The distance of the road from above is determined as follows:-

Map scale:- CD of the road = 8 cm If 1cm    represent 0.25 km

8cm    represents ?

8cm x 0.25km = 2km 1cm

Thus, the distance of the roads is about 2km.

Distance measurements for the curved elongated objects.

It becomes more difficult to obtain the conventional distance for the curved elongated object with the use of a ruler directly from the topographical map. Up on this challenge and others, one has to resort the use of the following enhancing tools to get the conventional distance of what required to be established. The enhancing tools include the following:-

A pair of divider

A piece of paper

A piece of thread

The use of a pair of divider

A pair of divider up on its nature is commonly used to measure short straight courses between points a long the elongated object. To make this, one has to do the following.

Identify the two recommended points of the elongated object on the topographical map given. The points can be identified by considering the given grid references, place names. Sometimes, both grid    references and place names and can be considered.

Divide the elongated object on the topographical map into convenient short straight sections.

Open your divider and measure the straight divisions (courses) along the recommended elongated object.

Add up all the measures to get total convectional distance of the elongated object.

The obtained convectional distance should be converted into the actual ground distance with respect to map scale provided.

The distance of the road above is obtained as follows:- AB=1cm; BC = 1.5cm; CD = 0.5; DE = 2cm; EF = 2cm

The total CD = 7 cm

Map scale, 1 cm represents 0.5 km Then;

If 1cm        represent    0.5km 7 cm    represent        ?

7cms x 0.5km = 3.5 km 1 cm

Thus ; distance of the road is of about 3.5 km

The use of a piece of paper.

A piece of paper can be used to measure either a short or long distances.

Procedure;

Take a piece of paper and fold it.

Put the piece of paper on the map and measure each small distance along the route.

Take the piece of paper to the linear scale on the map to have ground distance

Example;

The distance of the road below can be determined as follows:-

Distance determination with the use of a piece of paper is up on the following application:-

Thus; the distance of the road according to the application above is of about 4.5 km.

The use of a thread.

Procedure:-

Identify the two recommended end points of the elongated object whose distance is to be measured on the map. The two ends can be identified by taking into consideration of grid references, place names or both.

Take the thread and spread it along the elongated object from one end to another.

Take the thread to a ruler to measure the conventional distance of the elongated object.

Convert the conventional distance into ground distance with respect to map scale indicated on the map.

The length of the road from A to B is determined as follows.

Map scale; 1 cm represents 0.5 km

CD of the road = 11 cm

THEN;

If 1 cm = 0.5 km

11 cm = ?

11cm x 0.5 km = 5.5 km I cm

Thus; the distance of the road is of about 5.5km

AREA SIZE DETERMINATION.

Area size refers to a bigness or extent of coverage of any part of the earth’s surface expressed in square unit of measurements. For instance; the bigness of a water body, plantation, forestland, country and others of the same consideration.

Area size determination of any thing from the topographical map should take into consideration of the following two keys issues.

Map scale; The ratio of distance between the map and the actual ground represented. This enables to change of conventional measurements obtained on the topographical map into actual ground measurements.

The shape of the feature on the topographical map given whose area size is to be measured whether regular or irregular. This determines the method to be used to get the size.

Area size determination for regular features.

Regular features are those whose appearance well defined. They include; triangle, rectangles, square, circle, trapeze, octogon and others of the same reflection. To calculate the size of these regular figures, some one has to apply a relevant mathematical application with respect to the shape of the features observed on the topographical map.

Consider the following:-

Triangle.

Consider the following illustration.

The size of the area occupied by forest is calculated as follows:-

So long the forest land occupied the shape of a triangle, the relevant formula is as follows:-

*Map scale; 1cm represents 0.5 km

*According to the measurements of the feature on the map.

Base    = 6 cms

Heigh t = 14 cms Then;

½ x (6 x 0.5 km) x (14 x 0.5 km)

½ x 3km x 7km

21 = 10.5

2

Thus; the area size of the forestland is of about 10.5 km²

Rectangle;-

Consider the following.

The size of the area occupied by forest from the given topographical map is determined by the following application.

So long, the forestland occupies the regular shape of a rectangle, the relevant formula is given as follows:-

*Map scale; 1cm represents 0.5 km.

*According to measurements of the figure on the map,

*According to measurements of the figure on the map

Width = 4 cm

Length = 8cm

4 cm x 8 cm

(4 x 0.5 km) x (8 x 0.5 km) 2 km x 4 km = 8km²

Thus; the area of the forestland is of about 8km²

NOTE:

The two given above represent the other regular figures. It is therefore important for the students to be knowledgeable to relevant mathematical applications for calculating the size of the other regular figures up on observation on the topographical map.

Area size measurement for the irregular figures.

To determine size for the irregular features observed on the topographical maps, some onbe may resort the use of the following methods.

Grid square method

Stripping method

Geometric method

The grid square method.

It is the most popular and widely used method of determining area for irregular figures observed on the topographical map with reflection to actual areas represented. It is mostly used, if the given map

observed to have the vertical and horizontal grid lines on its face forming so perfect square as cross each other at right angles.

From above, the area size of the coffee plantation is calculated follows:-

Map scale    1cm represents 0.5 km

*Method    grid squares consideration

Actual size of the ground by each grid square determination.

According to the grid squares on the given map;

Width = 2cm

Length = 2cm

2 cm

2 cm

Then;

2cm x 2cm

(2 x 0.5 km) x (2 x 0.5km) 1km x 1km = 1 km²

Hence; Grid sguare = 1 km² Complete squares = 3

x 1 km2 = 3 km²

Incomplete squares = 11/2 = 5.5

* 5.5 x 1 km² = 8.5 km²

Thus; the area size of the recommended feature is of about 8.5 km².

Stripping method

By this method, part of the topographical map with reflection to the ground represented under consideration is divided into a number of convenient strips. It has to be followed by finding out the area size of each strip and have to be all added to get the entire area size of the feature.

Consider the following illustration:-

The area size of the lake is obtained as follows:-

*Map scale 1cm represents 0.5

Strip A: 8cm x 1cm

(8 x 0.5 km) x (1 x 0.5 km) 4km x 0.5 km = 2km²

Strip B: 10 cm x 1 cm

(10 x 0.5 km) x (1 x 0.5km)

(10 x 0.5 km) x 0.5 km = 2.5 km² 5km x 0.5 km = 2.5 km²

Strip C: 8cm x 1cm

(8×0.5 km) x (1 x 0.5 = 2 km²) = 2 km²

Strip D: 9cm x 1cm

(9×0.5 km) x 0.5km = 2.25km²

4.5km x 0.5km = 225km²

Strip E; 8cm x 1cm

(8 x 0.5 km) x (1 x 0.5 km) 4km x 0.5km = 2km²

Then;

2km² = 2.5km² + 2km² + 2km² + 2.25km² + 2 km² = 10.75km²

Thus; the area size is of about 10.75km² Thus; the area size of about 10.75km²

Geometric method.

It is by dividing the boundary area of the feature into a convenient number of mathematical (geometric) figures of like rectangles, triangles or combination of these figures on\over the same. It should be followed by calculating the area size of the forced geometric figures with respect to the used scale. At last the distinctive size should be added to get the entire area size of the feature.

Consider the following illustration;-

*Map scale    1 cm represents 0.5 km

Rectangle A

8cm x 18 cm

(8 x 0.5 km) x (18 x 0.5 km)

km x 9 km = 36 km²

Triangle B

½ x 18cm x 10cm

½ x (18 x 0.5 km) x (10 x 0.5 km)

½ x 9km x 5km

½ x 45 km = 22 .5 km²

Triangle C:-

½ x 16cm x 6cm

½ x (16 x 0.5km) x (6X0.5km)

½ x 8km x km

½ x 24km = 12km²

Then; 36km2 + 22.5 km2 + 12km² = 70.5 km² Thus; the area size is of about 70.5km²

EXERCISE

Qn. What is the length of the all weather road with loose surface from Grid 930352 to Grid 040339 in kilometers.

(NECTA 1999 —– Extract map Babati    Series Y 742)

Qn. Measure the lenghth of the major road from grd reference 886220 to grid reference 975192. Give your answer in kilometers. (NECTA 2004    Extract nmap of Mwanza sheer no. 33/2)

Qn. Calculate the area covered by forest in square kilometers. (Necta 2009    extract map of MPWAPWA sheet no 163/4)

Qn. Calculate the area of kisangara estate in square kilometers

(EZEB —– 2009……. Extract map of Kisangara sheet no 73/1)

Qn. Calculate the area covered by plantation agriculture in square kilometers (NECTA 1999    Extract

map Babati …… Series Y 742).

Qn. Find the actual distance of railway line from grid reference 860975 to 930039 in kilometers. (NECTA 2006—– Extract map of Mpanda    sheer no 153/3)

Qn; Calculate the area of Weru sisal estate. (NECTA 1997 – Extract map of Moshi    series Y 742)

Qn. Measure the distance of the Moshi – mweka road all weather loose surface road (grid 154309 to 135400) (NECTA 1997 – Extract map of Moshi    series Y 742)

Qn. What is the total area covered by the lake in square km?

Qn. Calculate the area of lake balangida gidaghangaat and give your answer in square kilometers. (NECTA 1998 —–Extra map of hanang    series Y 742)

Qn. Find the total area of the land of this Island found to the west of Easting 180 if the scale of the map to duced y half (DSM – Mock AN 2003    Extract map Nansio Island sheet 22/1)

Qn. Calculate the area of seasonal swap, south of nothing 080 and west of easting 690. Give your answer is square km.. (JICA    2009) – Extract map of utete)

MAP REDUCTION AND ENLARGEMENT.

The cartographic processes of minimizing and expanding the size of any map understood as map reduction and enlargement respectively.

MAP REDUCTION

As it has been pre described, map reduction is a cartographic process of minimizing the size of a map to provide smaller representation of the area.

To reduce the map the following as rules should be followed:-

All sides of the map i.e. the length and width should be reduced with the same number of times.

All drawings on the map should be reduced with the same number of times.

The scale has to be changed to become a comparatively smaller in order for it with respect to map to give the same ground measurement as the old map does.

The map has to be redrawn by using the reduction measurements.

Insert the details on the reduced map according to new reduction measurements. The transfer of details should take into consideration of the grid pattens, and if possible for making more accuracy, the diagonal lines can be drawn the grid squares.

Note:

The conventional symbols, signs and abbreviations should be reasonably small in order for them to fit onto the size of reduced map.

Impacts of map reduction.

The map size becomes smaller and thus gives smaller representation of the area mapped.

The map would become less detailed as it more selective due to the limitation of the map’s space.

The cartographic symbols, signs and abbreviation appear smaller.

The scale of the map becomes comparatively smaller.

Consider the given map and reduce it by ½

Procedure.

Consideration of the given map by studying it clearly.

Determination of the amount of reduction reduction factor is by ½

reduction of the map length

Length on the old map = 8cm

8 x 0.5 = 4cm

Hence; the new length = 4cm (iv)reduction of the map width

width on the old map = 8cm

8 x 0.5 = 4cm

Hence;the new length = 4cm

Reduction of the grid squares

Grid square on the old map = 2cm 2cm x 0.5 = 1 cm

Hence; the new grid square = 1 cm

Determination of the new scale

½ x 1/50,000 = 1/100,000

Hence; the new scale = 1: 100,000

Alternatively the new scale can be determined by the following application

3cm = 1 cm to km

3 km Or

4 cm = 1cm to 1 km

4km

Thus; the reduced map appears as follows:-

MAP ENLARGEMENT

It is a cartographic process of expanding the size of a map to provide larger representation of the mapped area.

To enlarge a map the following as rules should be followed:-

All sides of the map, i.e. length and width should be enlarged with the same number of times.

All drawings on the map should be enlarged with the same number of times.

The scale has to be changed to become comparatively large in order for it with respect to the map to give the some ground measurements as the old map does.

The map has to be redrawn by using the enlargement measurements.

Insert the details. The transfer of details should take into consideration of the grid pattens, and if possible for making mre accuracy, the diagonal lines can be drawn across the grid squares.

Note

The conventional symbols signs and abbreviations or initial should be reasonably large in order for them to fit onto the enlarged map.

Impacts of enlargement.

1. The map size become larger and thus, gives larger representation of the mapped area.

2. The map is likely to be more detailed as it is less selective due to the larger space of the map.

3. The cartographic symbols, signs and abbreviations may appear larger in size.

4. The scale becomes comparatively larger.

Consider the given map below and it enlarge by 2.

1:50,000

Procedure

Consideration of the given map studying it Clearly.

determine of the amount of enlargement. Enlargement is by 2.

Enlargement of the map length.

Length on the old map = 4cm 4cm x 2 = 8cm

Hence ; the new length = 8cm

Enlargement of the map width

width on the old map = 4cm

4cm x 2 = 8cm

Hence;the new width = 8cm

Enlargement of the grid square.

Grid square on the old map = 2cm 2cm x 2 = 4cm

Hence, the grid square = 4cm

Determination of the new scale

2 x 1/50,000 = 2/50,000 = 1/25,000

Hence; the new scale = 1:25,000

1:25,000

Alternatively the new scale can be determined by the following application.

Map scale = Map distance

Ground distance

8cm = 1cm to 0.25cm 2km

Qn. (a) Outlining your steps redraw provided (1:50,000) to a scale of 1:100,000 and indicate the following features:-

The forest area, Songoro and chimumbu hills, lake Duluti, Nkoaranga hospital and all weather road bound surface.

(b) Examine the two maps and comment on the impact the change of the map scale has on the map area and its contents.

(DSM – MOCK, 2002:Extract map of TENGERU: (sheet No./ 55/4Ed)

Qn. (a) Calculate the approximate area in square kilometers of the contoured map if its scale changed to 1:100,000 (NECTA 2001, Extract map of Kondoa – sheet # 104/4)

Qn. Redraw the map north of northing 120 and west of easting 650 by the scale of 1:25,000 and on it indicate woodland and seasonal swamp.

JICA ===2009) Extract map of ulete)

Qn. Draw a map of district found at the western part of the map by using the scale of 1:100,000 and on its show the following.

Boundary of the district

Mwanza – Shinyanga road

usagara – Fela station road

Railway line

Ngeleka hill, jijawenda hill and kagela hill

Out crop rock around jijawenda hill.

Bridges along Fela – Mwanza road (NECTA 2010)

MAP ORIENTATION

POSITION LOCATION ON TOPOGRAPHICAL MAPS

The position location of geographical features on topographical maps with reflection to actual areas represented can be established by employing one or more of the following methods:-

1. Place naming

2. The use of latitude and longitudes

3. Grid reference

4. Bearing and distance

Place naming

By this, method names of places on the topographical maps and up on the earth’s surface can be used to give the position location of a point, feature or another place e.g. the Yanga Sports club head office is at Jangwani.

If place naming method is used for giving position location of any geographical feature on he

topographical map and up on the respective actual area represented on the earth’s surf ace, should

meets the following conditions:-

The name of a place to be should be unambiguous i.e. some times more than one places may share the same name.

The name to be located should be of of significance to a person.

NB:
So long the place naming method is facing a problem of ambiguity, it can be dissolved supplementing it with another method of giving location like that of grid reference or direction. E.g. the school is at Ruvu, GR 432675.

The use of latitude and longitude:

It is the most useful geographical method of giving position location on the map and up on the earth’s surface. These measurements are always needed in actual making of the accurate maps. Nearly all maps indicate these along their edge though not all show these in more detail.

Both, latitudes and longitudes are really angular distance measured accurately from the centre of the earth and are expressed in degrees and further divided into smaller measurement units of minutes and seconds.

Latitude is an angular distance measured northward and southward of the line) Longitudes are the angular distances eastwards and westward of the prime meridian.

The latitudes and longitudes are commonly used to locate the position for the wider features on the small – scaled maps or atlas maps on which these established more detailed.

Procedure of giving latitudes and longitudes.

Firstly establish the degrees of latitudes of a place where is located from one edge to another on the map

Establish the degrees of longitudes of the place on the map from obne edge to another.

Combine the degree reading of both latitudes and longitudes to give the proper position location of the place.

From above Tanzania located in Latitude and longitude position of 10 30′ sand 300 to 400 E.

Grid reference:-

The use of latitudes and longitude becomes increasingly difficult for larger scaled maps. For this and others, map makers have devised a quicker and easier method known as grid reference.

A grid is a network of the evenly spaced vertical and horizontal lines drawn on the map face. The lines drawn perpendicular to one another and cross at right anglesand form the so perfect squares.

All vertical lines are called easting, because of being numbered eastwards, while the horizontal lines are numbered northwards referred to northing.

The establishment or reading of the grid reference, it has to start by producing the numbers of easting, and then those of northing.

Grid reference can be given in four figure numbers, if the position to be located is at the exactly intersection of the vertical and horizontal grid lines. It should be in six figure numbers, if the position to be located is not at the intersection of the vertical and horizontal grid lines. However; it is always much better for the grid reference be in six figure numbers regardless of the cases.

Point T is located at GR 403705

Point S is located at GR 437692

Note

The grid lines belong to maps. It is thus, have no reality on the ground. They do not even relate as do latitudes and longitude.

Bearing and distance:

The method is mostly used to establish the location from another position by giving the degree angle measure clockwise from north and the distance of an observation line between the two positions.

Bearing is the degree angle of an observation line connecting two points on the map with reflection to

an area on the earth’s surface measured clockwise from north direction.

Distance is the length of a space in between the two position points on the map with reflection to an

actual area on the earth’s surface represented.

From the above; x is located at bearing and distance of 45⁰ and 12.5 km respectively.

Example:-

Determine the location of point B from point A Bearing determination

Procedure:

Identify the two recommended points on the map by considering the grid reference or place names given. Some times both, grid reference and place names can be provided together.

A straight line has to be drawn to join the two end points on the map. The line

represents an observation sight between the two positions in the mapped area on the earth’s surface represented.

Establish the four cardinal points at the position of observer. The establishment of the cardinal points should take into consideration of the north direction indicated on the map. On some of the topographical maps, the north direction is given by means of a true north.

Take the protector and measure the angle of an observation line that connects two position points clockwise from north direction.

The bearing of point B from point A is of about 305⁰

Distance determination

Procedure

Take into consideration of the map scale

Measure the conventional distance (CD) of the observation line that connects the two points on the map.

Convert the CD into AD with respect to map scale

From above the CD = 10cm

Scale; 1cm represents 0.5 km

Then;

10 x 0.5 km = 5km

Thus; point B is located at bearing and distance of about 305⁰ and 5km respectively from point A.

Calculate the Bearing

Backwards bearing :–

It is the reverse of the bearing of an object taken in front of the observer’s position along the observation line is called forward bearing. While the bearing of an object measured clock- wise from north direction backwards to the former observer’s position along the same sight line is called backward bearing. It is thus, backwards bearing s defined as the degree angle of the object measured backwards to the former observers position.

Backward bearing of an object is obtained by measuring the degree angle of an observation line clockwise from north direction backwards to former observer’s position. This can be illustrated as follows:-

Mark the four cardinal point at the observed object whose backward bearing to be established.

Take a protector and measure the degree angle of an observation line clockwise from north direction

Example

The backwards bearing of point b from point A can be established as follows:-

Thus; the backward bearing of point b from point A is of about 1250 Note

If the forward bearing of the object has been established, the backwards bearing can be determined by mathematical procedure.

BB = FB + 180⁰ if the FB IS LESS THAN 180⁰

BB = FB – 180⁰ if the FB IS GREATER THAN 180⁰

From the above case The FB = 305⁰

305⁰ (FB) > 180⁰ THUS ; The BB = 125⁰

Significance of the backward bearing

Backwards bearing is determined purposely to check the accuracy (correctness) of the forward bearing which has been taken in front of the observer’s position to an object along the sight line. It is checked by observation the difference in degrees between the BB and FB.

Always the standard difference should be 1800 if the difference is less or greater than 1800 the reading has been subjected to an error and thus needs correction to make proper determination.

Correction of errors

Correction of errors is attempted with the use of the mean error but considering the varied cases. Mean error is computed by making the following application:-

The correction of errors with the use of mean error is done by making the following applications:-

When BB > FB

When BB < FB

DIRECTIONS

Direction means the course or a line along which a person or thing moves or locks or which must be taken to reach a destination.

Direction on the map can e given in four, eight or sixteen cardinal points of compass and their corresponding angular bearings.

Note:-

One land direction measured with the use of magnetic compass. The magnetic compass has a needle which always points to the north.

ALIGNMENT OF ELONGATED OBJECT.

Alignment is defined as a general direction and bearing of an elongated object on the map and up on the earth’s surface measured from the central position along the straight line. Elongated object can be of like that of a road, railway, ridge, coastline, river and others of the same nature.

Alignment is best described by stating both, direction and bearing E.g. the road aligns from 45⁰ to 225⁰ (SW)

Steps involved in giving the alignment

Identification of two end points on the topographical map given. The end points can be identified by taking into consideration of the grid reference or place names given.

Drawing of the straight fine line using a ruler and pencil to join the two points.

At the central point of the drawn line mark the four cardinal points.

Take a protector and measure both degree angles in which the drawn straight line trends.

The alignment the coastline is from 068⁰ (ENE) to 248⁰ (WSW)

EXERCISE

Qn. Calculate the forward and backward bearing of Ryamugasire island grid 930340 from buhare home economics training centre grid 868324 (NECTA 2005 – Map extract of musoma sheet 12/2)

Qn. Calculate the forward and backward of Songea town at Grid reference 829169 (NECTA 2003 – Map extract of SONGEA sheet 299/1)

Qn. The compass bearing takes from a fishing boat to Samgoro hill and pump house Gr 045647 were 145⁰ and 122⁰ respectively.

Qn. By using grid reference write the position of the fishing boat.

Qn. Find the true bearing of the Samgoro from pump house (NECTA – 2002 the map of part of KENYA –NYAKWERE)

Qn. The compasses bearing of Lugongo and Kiamera hills were 1300 and 1490 respectively. These bearings were taken from a steamer on the lake.

Qn. Give the grid reference of the position of the steamer

(ii) Measure the distance in kilometers from the position of the steamer to Kaswanga pt : (NECTA 1994-The map extract of Rusinga island)

Qn.An amateur surveyor recorded 87º as forward bearing from Goi Hill to Sangasanga hill, and 263 as his backward bearing.

Correct the discrepancy of these readings.

State the importance backwards bearing.

(NECTA-2001, the map extract of KONDOA (sheet104/4.

Qn. Give the bearing of:

The Masonic Lodge from Kibwesi

Tanzania packers factory from kiutu peak .

In each case, give the backward bearing.State the rule that enable you to check the correctness of your bearing (NECTA 1992 Extract, map of Arusha)

Qn. Determine the trend alignment of part from Raska zone grid reference 137417 to grid reference 148360 (NECTA – 2008 extract map of TANGA sheet 130/1)

Qn. Locate the position of Njoro school (NECTA 1997 – Extract map of Moshi Series y. 742)

Qn. (a) Find the trend of the major road from mwanza city to Musoma.

Show the alignment of the railway line (NECTA 2004 – Extract map of Mwanza sheet # 33/2)

KINDS OF NORTH INDICATED ON TOPOGRAPHICAL MAP.

On most of the topographical maps, varied north are shown and these include rthe following:-

Magnetic north (MN)

True north (TN)

Grid north (GN)

Magnetic north

Magnetic north is the one given by the line of half arrow head on the map representing the direction of

magnetic pole (earth’s magnetic field) from the mapped area.

Magnetic pole is position of natural attraction of global magnetism

The direction of magnetic pole is detected by a needle of magnetic compass in the mapped area by the time of map construction. The needle of the magnetic compass points towards the direction where the global natural point of magnetism is located from the area to be mapped.

The north line on most of the African maps is not uprightly vertical . It is slightly vertical towards west as the global natural point of magnetism is located in America.

The natural point of global magnetism is found off the coast of Boothia peninsular, the north of Canada nearly price of Wales and In South is in Victoria land Antarctica.

However; the direction of magnetic pole shown on the map by magnetic north, is irregular as the natural attraction of magnetism is in water and the rate of change per year is noted.

True north

True north is the one given on the map as a star head line to represent the direction of global North pole (90⁰ latitude) from the mapped area. It is parallel with the lines of longitudes.

The north pole is where all lines of longitudes meets. True north is the most useful north to geographic and it is mostly referred in the determination in position direction on the topographical map and up on the actual area represented.

The direction represented by true north does not change over the time because, the North pole is steadly constant in position.

Grid north

It is the unpointed north line given on the map, which follows the system of easting gridlines. This does

not represent or show anything on the earth’s surface and that is why given by the un pointed line.

Magnetic variation:-

Magnetic variation is an angular distance in a place from the direction magnetic pole to the direction of north pole. i.e. the measured angular distance from true north to magnetic north on the map with reflection to the actual area represented.

Always the direction of magnetic pole as represented by magnetic north on the map changes, but does not coincide with the direction of north pole (true north) This makes a considerable angular distance in between of the two direction does not remain the same at the time due to the irregulaties of the

magnetic field on the earth’s surface and thus, give to magnetic variation.

Magnetic variation is 7⁰ 14 W

Magnetic bearing:-

It is a degree angle of an observation line of a place to another place measured clockwise from the direction of magnetic pole. This is not rigid as the direction of magnetic pole is irregular.

True bearing:-

It is a degree angle of an observation line of a place to another place measured clockwise from the direction of north pole. The angle on the map is measured clockwise from north pole towards the line of the observation. This is rigid as the direction of North pole from any place is steadily constant.

Magnetic variation projection:-

For some wishing to determine (project) magnetic variation of a place on the earth’s surface with

reference to the previous one,has to make the following fundamental steps.

Data analysis as per the details (content) available.With respect to this, the following should be recognized.

The previous recorded magnetic variation.

The date when the last magnetic variation has been recorded.

The current date whose magnetic variation to be projected.

The rate of change per certain given defined period of time like, year, month etc

Determination of the time interval by subtracting the old date from the new date. i.e.

Time interval = T2 – T1

Determination of the total change of magnetic variation by multiplying the rate of change with the determined time interval.

Get the new magnetic variation of the place by making addition or subtraction to the past magnetic variation. Addition is made if there is positive change: while, subtraction is made if there is negative change.

Exercise

Qn. Town Z had magnetic variation of 32⁰ 42 by march 1980, what was the new magnetic

variation of the place by December 1990, if the rate of change is 10′ per annum positively.

Qn. Town X in west Africa had MB and TB of 450 23’12” and 250 34’57” respectively by January 1990. If the rate of change of the direction was 15′ per annum negatively, calculate the following by July 2005.

Magnetic variation

True bearing

Magnetic bearing

Qn. (a) Differentiate between magnetic bearing and True bearing.

(b) Town X had magnetic variation of about 340 21″by November 1982. What was the new magnetic variation of the same town by February 1993, if rate of decrease stood at 15′

annually.

Qn. Differentiate between the magnetic north, True north and grid north (NECTA 1995) Qn. (i) Define true bearing and magnetic bearing.

(ii) January 1945 the magnetic variation over town X.

Grid bearing

It is a degree angle of an observation line of a place to another place measured clockwise from the grid north.

The conversation of magnetic bearing into true bearing

To convert magnetic bearing into true bearing, some one has to take into consideration of the direction of magnetic pole relatively to the direction of north pole.

If the direction of magnetic ole is to west of north pole direction on the map and up on the

earth’s surface, true bearing of the place is obtained by applying the following formula.

TB=MB – MV

45⁰ – 15⁰ 26 = 29⁰ 34′

Hence: the TB is of about 29º 34′

While:

MB = TB + MV & MV= MB – TB

If the direction of magnetic pole to east of the north pole direction on the map and up on the area represented, the true bearing is obtained by applying the following application.

45⁰ + 08⁰ 18’=53º18′

Hence,The TB is of about 53⁰18′ While:

MB = TB – MV & MV = TB – MB

EXERCISE

Qn. 9’56 If the annual decrease rate stood at 5’Find the magnetic variation of the same town in October

1966 (NECTA 1989)

Qn. (a) Define true bearing and magnetic bearing

(b) The true bearing and magnetic bearing aver town by January 1990 were 53⁰ 42 and 58’21” respectively, What can be the projected magnetic variation over the same time by july 2010 if the rate of change wood at 15’E

Qn. (MOCK)

(i) Define true north, grid north and magnetic north

(ii) Town Y had MB and TB of about 27036′ and 540 of 23″ respectively by September 1982. Determine the MV. MB and TB of the same town as it was February 1993 if the rate of change stood 18’w.

UNDERSTANDING FEATURES ON MAPS RELIEF REPRESENTATION ON MAPS

Relief refers to the physical appearance of an area by contrasting landforms. Or Variation in

shapes and forms of an area over the earth’s surface.

The land forms which make the physical appearance of an area called relief features. These being landforms have defined shape and heights above the sea level.

The cartographers use to show the relief features on the maps by employning certain methods which reflect their shape and heights in response to the physical appearance of the area.

The main methods employed for this purpose include the following:-

Contouring method.

The method involves the drawing of contours (isohypes) on the map face. Contour is an imaginary line drawn on the map face connecting all points of exactly equal height above the mean sea level. The first contour map was introduced in 1791.

Contours as used for relief representation on large scaled maps (topographical maps) reflect shape, size and height of landforms of areas represented.

Properties of contours as used for relief representation.

Contours on the maps are numbered either in Meter or feet. The numbers represent the attitude values of relief features in the region mapped.

There are two numbering the contours

The contour numbers are written on the higher Side of the contour line.

The contour numbers are placed in the contour lines

Contours are drawn in a specific interval on the map.

Contours of different elevations do not cross each Other.

When Contours lie closely to one another indicate steep slope, and if observed to lie far apart indicate a gentle slope. Based to this, contours of different heights may join to form a single contour line where contours are not observed over wider part, implies the landscape is widely flat.

Usually contour lines tend to join around where there is the presence of a rounded landform like; a hill, plateau, escarpment and others.

Contours form V shape pointing up or down stream to indicate the presence of a river valley or spur respectively.

Merits of contours

1. Contours are the most popular and widely used method for showing relief on topographical maps.

2. Contours on a topographical map can be association with other methods of showing accurate heights of the relief features of an area represented. Provide the basis for hypsometric map construction.

3. Contours on a topographical map can be associated with other methods of showing relief like; spot heights, trigonometrical point and benchmarks.

4. Contours on a topographical map do not hide other details.

5. Contours aid in making of some ground measurements from the topographical map.e.g/gradientdetermination

6. Provide the basis for cross section drawing from the map. Setbacks of Contours

7. Some times, contours fail to show certain highest heights due to the limitation of the vertical interval used. Such heights can be shown by means of spot or trigonometric point.

8. Some of the landforms are not capable for being represented by means of contours e.g. coral reefs, levees and other of the same refletion .

9. Contour are not suitable for showing relief on a small scaled map.

10. It needs high skill to make interpretation on the relief features by reading the contours.

11. It needs high skill to produce contours on map spot heights and form lines should be initially established ahead to contours.

12. It becomes difficult to determine the exact altitudes of such parts which are not crossed by the contours.

13. The altitude of such parts given in estimation basis.

Setbacks of contours

Some times contours fail to show certain highest heights due to the limitation of the vertical interval used.such heights can be shown by means of sport height or trigonometric point.

Form lines

A surveyor has some times to draw contours by eyes by estimating where the contours would run between two sport heights or by sketching them in approximately (interpolating). The lines drawn in this way are called forms line. Hence forms lines are defined as the dotted and unnumbered lines drawn on the map face joining points of approximately the same heights.

Form lines are not always plotted at fixed interval and these provide the basis for establishment of contours or layer units on the map.

Layer tinting.

(Layer colouring)

It is one among the most useful methods for showing relief on maps. It is by indicating distinctive colours on the map face, to contrast zones (Bands) of altitudes. The method is mostly used for Relief representation on small scale maps (atlas maps).i.e. on maps that represent very wider parts of the earth’s surface.

A map that involves the system of colours to indicate relief is called hypsometric map. The method was firstly introduced in 1878.

Any layer –tinted map should carry a key to interpret the different colour for varied bands of altitude. The common colours used for this purpose include the following:-

Blue; represents water body. Light blue means Shallow water and dark blue means deep

Green, indicates low land of either coastal plain or river valley. Pure green colourrepresents much low land with altitude from 0-200m; while; light green represent lowland of high altitude from 200-500m).

Yellow, indicates high land. Whitish yellow represents high lands of low altitude from 500- 1000m); while pure yellow is for higher land with height from 1,000-2000m).

Brown; indicates highest mountain or area with permanent ice.(2000-4000m).

Red or pink, indicates very high elevation with height above 4000m

Merits of the layer tinting method.

1. It makes a map look impressive and attractive to the users.

2. It is useful method for showing relief on a small scale map.i.e on maps which represent wider areas.

3. It is associated with the method of trigometric point. The trigonometric points provide specific exact highest altitude of particular part.

4. They give quick information to map user so long the colours easily seen on the map.

Demerits of layer tinting method.

1. It shows general altitude i.e. does not give the exact height of specific or particular point.

2. It is more expensive to produce the layer colored map

3. The method does not reflect the shape of relief features of an area on the map.

4. Always colours carry certain people’s mind. It is therefore, someone may have wrong interpretation. e.g the presence of green colour on the map may makes some one to reflect the presence of thick ever green forest.

5. If colours have already been used for layer tinting on the map ,can be used for other purposes on the same map.

6. It is not a complete method by itself. It relies on the presence of contours or form lines to provide the basis for colouring.

Hachuring

The method involves the use of hachure.

Huchure is a series of small lines drawn on a map face showing the direction and steepness of slope. The lines are drawn to follow the slope of the ground or direction of the slope on which water would run. It is old method of showing relief on maps and it was devised by L.C Muller in 1788. It was later improved by Austrian topographer Johann George Lehman in 1799.

Merits of hachuring

1. Hachure easily seen on the map and thus give quick information about the features represented.

2. Provide pictorial view of the relief features on a map.i.e they can successively communicate quit specific shapes of terrain.

3. Show clearly the direction of slopes on the map. i.e. They provide a general sense of steepness.

Demerits of hachuring.

1. Hide other details seen on the map and thus give quick information about the features represented.

2. Hachure on the map is non numeric.i.e.are not associated with height numbers of relief features represented. Thus, the map users are not in position to detect the relief heights by studying hachure.

3. Greet skill is needed to produce hachure on a map.

4. The hachure may not be maintained on constant scale.

5. The method is dying out. It is not much used for relief representation on the modern constructed maps.

Hill shading.

It is a method of showing relief in which some parts of the map are shaded to indicate the presence of hill, as they would appear if a light were shining on them. Usually, the slopes which face light are shaded lightly while those facing away are in shadow.

Merits of hill shading

It gives pictorial view to the map user about the hills of an area shown on the map .it thus becomes easier to understand.

Make a map looks impressive and attractive to the users

Demerits of Hill shading.

Does not give heights of hill shown on the map.

The shades indicated on the map might hide other details.

It becomes difficult to determine the gradient of the hills represented so long, the hill shades not given with height numbers.

May not easily maintain on constant scale of the map.

The use of physiographic diagrams.

The method involves the drawing of diagrams on a map face reflecting the physical slope of the relief features like hills and mountains as they have been observed in the area. This conventional representation of land forms on the map, gives an impression of viewing the landforms in three dimensions.

The physiographic diagrams are also known as pictorials.

Merits of the physiographic diagrams

The physiographic diagrams if appear on the map, become impressive and attractive to the map users.

The diagrams provide more pictorial view of the relief features representated as they more reflect the shape of the land forms represented. It is thus, becomes so much easier to understand.

They are easily seen on the map and thus easy to read and provide quick information to the map users.

Demerits of Physiographic diagram

Hide other details.i.e may not make other details for the represented area to appear on the map.

Physiographic diagrams are non numeric as do not provide the heights of landforms represented thus, they do not make the map users to understand the altitudes of the represented relief features.

Only limited landforms can be shown. i.e. not all landforms can be shown by this particular method.

Not good method for the accurate maps as the physiographic diagrams cannot be maintained on the constant scale of the map.

The method is no longer used for relief representation on the modern constructed maps.

Trigonometric point.

It is a very small triangle conventional sign with a dot at its centre and value number beside to it. This is non imaginary method for relief representation on the map as trigonometric points established up on the presence of height ground station. (Trigonometric station) on the ground. It is thus, trigonometric point is indicated on the map provided the represented area has trigonometric station.

The number given with the trigonometric point represents the highest altitude of the land scape

Merits of the trigonometric point.

1. It is easy to indicate trigonometric point on the map by the cartographer

2. It is non imaginary method for relief representation on the map.

3. Enables the map users to recognize the highest relief height very easily.

4. It shows the accurate relief height as it was measured more accurately in are above the sea level or from a recognized reference point of bench mark.

5. Sometimes. it assists the contouring method in showing certain relief heights due to the limitation of the contours interval used.

Demerits of the trigonometric point.

1. Not easily seen on the topographical map. It is as the topographical map shown the general geographical details of an area represented.

2. Trigonometric point on a map does not give the shape of the relief feature represented.

3. They are selective for showing only the highest heights of the relief features represented.

Spot height

It is a conventional dot (point) together with the height number on a map face. It serves imaginary method for showing relief heights as have been measured above the mean sea level. The number shows the height of a relief feature shown on the map

Merits of the Spot height.

1. It is easy to indicate spot height on the map by the cartographer.

2. Enables the map users to recognize the relief height very easily.

3. It shows the accurate relief height as it was measured more accurately in the area above the sea level or from recognized reference point of a bench mark.

4. Sometimes; it assists the contouring method in showing certain heights due to the limitation of the contours interval.

5. It shows the heights of hill summits as well as points along the interested structures

Demerits of spot height.

Not easily seen on the topographical map. It is so as the topographical map shows the general geographical details of an area represented.

Spot height on a map does not give the shape of the relief feature represented.

It is imaginary method for showing relief on a map.

Bench mark

It is a surveyor mark unit indicated on a wall, pillar, or building used as reference point in measuring altitudes.

Or

a point of reference used by a surveyor in measuring altitudes.

Bench marks indicated on maps following the presence of such marks in the are mapped.

Bench marks on maps appear by the conventional letter of BM together with height numbers measured on the ground.

Categories of Bench marks.

Bench marks indicated on the map and up on the landscape represented are extremely varied.

Some have been established to provide permanent reference in measuring altitudes, while others provide short terms reference to measure altitudes by doing surveying. With respect to this, bench marks are categorized into two and include the following:-

Temporary bench mark

These established so closely to the site of surveyor to have continuous reference in surveying process. They use to appear by conventional letters of TBM. However; these on topographical maps do not commonly appear.

Ordinance bench marks.

These are the fixed bench marks indicated on the map with reflection to the actual area represented.

They provide permanent reference in measuring altitudes of other interested point or areas.

Merits of the bench mark.

1. It is easy to indicate it on the map by the cartographer.

2. It is non imaginary method for relief representation on the map.

3. It shows the accurate relief height as it was measured more accurate on the landscape above the sea level.

Demerits of the bench mark.

1. Not easily seen on the topographical map. It is as the topographical map shows the general geographical details of an area represented.

2. Bench mark on a map does not give the shape of the relief feature represented.

Asses yourself!

Are you able to describe the different methods of showing relief on maps?

Do you understand the application of the different methods as used for relief representation?

Are able to narrate the merits and demerits of the methods as used to show relief on the map?

EXERCISE

Q. (i) why contours are considered to be the most useful ways of showing relief? (NETA 2007).

(ii) Explain the demerits of using hartures to represent relief on the map (NECTA – 2007).

Q. Outline and describe the different methods employed by the map maker to show the exact height of relief features on the map (NECTA 1997).

Q. (i) Describe the methods used to portray the relief features on the map.

(ii) Which other methods may have been used to depict the relief features on the map? (NECTA 2003, The map extract of Songea sheet 299/1).

Q. Describe any two demerits of hill shading as a method of representing relief on the map. (NECTA 2002).

CARTOGRAPHIC SYMBOL AND SIGN

Topographical maps are drawn for geographical studies do not show the natural and artificial features as they appear in real life on the earth’s surface. Some of the selected conventional signs and symbols used to serve this purpose, and these are collectively referred to cartographic symbols and signs.

Hence the cartographic symbols and signs are defined as the conventional signs and symbols inserted on a face of a topographical map representing the natural and artificial features of an area mapped.

They act as language of map to provide geographical details of areas represented.

The cartographic symbols and signs are used to represent the natural and cultural features on the topographical maps, should have the following qualities.

Should be correctly and clearly shown on the map.

They should be easy to read.

Easy to understand and interpret

Note.

Symbols are those used in maps which look like the natural and artificial features represented, while the signs are those which do not look like the natural and artificial features represented.

CLASSIFICATION OF THE CARTOGRAPHIC SYMBOLS AND SIGNS

Cartographic symbols and signs are extremely varied and thus, classified into different types. They are classified according to their form of appearance on the map, and nature of data shown on the map.

According to the form of appearance, cartographic symbols and signs classified into the following types:-

Point cartographic sign:-

These are the cartographic signs in form of dots inserted on the map face. They are employed to show positional data on the mp. i.e. show a specific point on the map and up on the earth’s surface there a certain object or place occurs.

Line cartographic symbols:-

These are the conventional symbols, which take linear distinctive form of appearance on the map. They are employed to represent the elongated objects on the map with reflection to an area represented.

Examples of the elongated objects represented by the line cartographic symbols are of; power transmission lines, roads, railway and administrative boundaries.

Areal cartographic sign:-

It is the conventional representation established on the map by which a continuous distinctive shade or tone employed to show a feature that covers wider part. Such features include; swaps, plantation, lakes and others.

Pictorial (descriptive) cartographic symbols:-

The conventional symbols given on the map to portray the shape of the features represented. e.g. the symbols for church, mosque, bridge and others of the same reflection.

Geometric cartographic signs:-

The conventional signs in form of geometric figures of like square, triangle, circle and other e.g. the trigonometrically point.

Letter or number cartographic signs:-

The conventional representing on a map in which one or more letter or numbers given. E.g. such for school, ch-for church, pwd – for public work department and others.

According to the nature of the features represented, cartographic symbols categorized as follow:-

Relief cartographic symbols:-

These are the symbols inserted on the map, representing the relief of an area. They include; contours, hachure, spot heights, trigonometric point and others.

Transportation cartographic symbols:-

The conventional signs representing transportation systems of areas represented of like; roads, railways, air fields etc.

Vegetation cerographical symbols:-

The symbols for natural and planted vegetation.

Settlements cartographic symbols:-

The symbols, which represent both rural and urban settlements of an area on the map. They include round black dots for rural settlements and black rectangle blocks for urban settlements.

Water bodies (hydrograph) cartographic symbols.

These given on the map to make representation of the water body systems.

Asses yourself!

Are you able to define cartographic symbols and signs?

Do you understand the main qualities of cartographic symbols and sign?

Are you able to describe the different types of cartographic symbols and signs according to different elements of variation?

CROSS SECTION, INTERVISIBILITY, HORIZONTAL EQUIVALENT AND GRADIENT.

CROSS SECTION

Cross section is a transect diagram or topographical profile of an area drawn on a paper with details taken from the topographical map to show the structural appearance of the landscape in between of the two points. It is alternatively known as relief section or topographical profile.

Cross section is of two types and include; the simple (sketch) and annotated cross sections.

Simple-cross section is the one not drawn to scale and is made to show the general appearance of the landscape between the given points in terms of relief.

Simple cross section is drawn after estimation of the general rise and fall of the landscape. The estimation is done after the study of the contours on the given map. Beside to this,

altitudes along the vertical lines not given.

An area to be sketched.

Simple cross section from A – B

The annotated cross section is the one drawn to scale and in which the position of important places and features indicated more accurately. It is also known as accurate cross

section.

The significance of a cross section.

1. Provides a clear pictorial view on the structural appearance of area in between the two places. With respect to this, a person may easily determine types of slope in the area and the appearance of the area whether undulating or un undulating.

2. It is useful for indivisibility determination between two points in the area. This is made possible as a cross section shows physical appearance of an cross section shows physical appearance of area and if clearly observed, the judgment of indivisibility becomes easier.

3. It shows clearly the altitudes of the different parts of the landscape in between of the two points in the area.

4. Cross section aid in making of gradient determination of the sloped landscape by relating the VI to HE.

CONSTRUCTION OF THE CROSS SECTION

The construction of cross section should fundamentally follow the following significant steps.

Identify and mark the two end points to be sketched on the topographical map. The points can be identified by taking into consideration of the grid references or place names given.

e.g. A and B.

2. Draw the straight line with the use of a ruler on the map to join the two identified points.

3. Take a piece of paper with a straight edge, or fold it to get straight edge and place along the drawn straight line on the map. The piece of paper has to be slightly longer than the length of

the line joining the two end points.

On the piece of paper mark the following important details.

The two end points, which have been identified on the map.

Where every contour line cuts the line.

The contour heights.

The important landscape feature of both, natural and cultural features.

Find the appropriate vertical and horizontal scales. The vertical scale is determined as follows:-

According to the traverse on given contoured map:

Thus; VS, 1cm represents 100m.

Vertical scale shows the relationship of height between the cross section and the actual landscape represented.

Note.

The graph space for the vertical distance of cross section lies up on a decision. Graph space should conditionally produce the vertical scale that can not results into vertical exaggeration that appears more than 10 or less than 5 as related to horizontal scale.

The horizontal scale remains to be the same to that used on the map. This provides the relationship of horizontal distance to actual ground represented.

5. Construct the framework for drawing the cross section. The framework should have both vertical and horizontal line distances. The horizontal line distance is determined by the length from one point to another on the map. The measurement of the vertical line has to correspond to the decided graph space.

Take the piece of paper which has been marked with the map details for cross section, and place along the horizontal line distance of the framework. Relate the height numbers to those allocated along the vertical line distance.

7. Connect the plotted points with pencil using the free hand to develop the structural appearance of the landscape.

8. Finish the cross section by including the following:-

Heading; To show what the cross section is for about.

Natural and cultural features; These if clearly indicated show the clear outlay of what is represented by the cross section.

Vertical scale; This shows the relationship of altitudes between the cross section and actual ground represented.

Horizontal scale; This shows the relationship of horizontal distance between the cross section and landscape represented.

Vertical exaggeration; It shows the relationship between vertical and horizontal scale of the cross section.

Key, if necessary.

North direction.

The source.

Horizontal scale ; 1:50,000 Vertical scale; 1:10,000

VE = 5

VERTICAL EXAGGERATION

A cross section by its nature has both, vertical and horizontal scales. The vertical scale is nearly always subjective, while the horizontal scale is steadily constant. The vertical scale by being subjective, it can be magnified. The amount of magnification of the vertical scale over horizontal scale is known as vertical exaggeration. Vertical exaggeration is thus, defined as the amount of times by which the vertical scale is larger over horizontal scale.

Or

The relationship between the vertical scale to horizontal scale of cross section.

Vertical exaggeration is very important in cross section drawing as it determines the shape of the features represented on the cross section.

The standard vertical exaggeration of the cross section drawn from most of the topographical maps with scale of 1:50,000, is that which does not exceed 10 units and not less than 5 units.

Vertical exaggeration is principally determined by applying either one of the following two principle formula:-

Example:-

If a cross section has the horizontal scale of 1:50,000 and vertical scale of 1:10,000, whose vertical exaggeration is determined as follows:-

According to the cross section:-

Horizontal scale = 1:50,000

Vertical scale = 1:10,000

Then; 50,000

10,000

Thus, the VE = 5. This implies the vertical scale is larger for 5 times to Horizontal scale.

INTERVISIBILITY

Indivisibility is the act of establishing whether the two positions in the area as observed on the map visible to one another or not.

A good way of realizing the indivisibility of two points on the map is by drawing a cross section from one point to another to view the structural appearance of landscape. On the cross section, draw a straight line called sight line to connect the two end points.

If the straight line passes clearly between the two points, it implies the sighting from one point to another is not obstructed and hence, the two positions are    intervisibility.

If the land rises high above the sight line, implies that, the sighting from one point to another is obstructed thus, the two positions are not intervisibility.

Factors affecting indivisibility.

Interivisibility between points on the map and up on areas on the earth’s surface effected by the

following factors.

Relief; Natural features like mountain, hill and others in between of positions, affect intervisibility.

Vegetation; presence of thick forest in between of positions also affects intervisibility.

Buildings; the presence of tall buildings in between two positions also hinder intervisibility.

HORIZONTAL EQUIVALENT (HE).

Horizontal equivalent refers to a horizontal distance of the sloped landscape in relation to its vertical height.

Horizontal equivalent can be high, low or nil depending on the degree of a slope steepness.

Gentle slope; gives higher horizontal equivalent. Steep slope; gives low horizontal equivalent.

Vertical slope; gives low horizontal equivalent

Horizontal equivalent is worked by converting the CD into AD with respect to map scale.

Example:-

Scale is 1cm=½km CD = 10 cm

10 x½km =5 km Or 5000m.

Thus; the horizontal equivalent is 5,000m or 5km.

GRADIENT

Gradient is a degree of slope steepness; or the ratio between the vertical interval (increase) to horizontal equivalent; or the amount of rise or fall in meter or feet of the land in relation to horizontal distance.

Gradient is determined by the following principle formula:-

Where by:

VI=vertical interval; It is the difference in height meter or feet between the highest and lowest altitudes of the two recommended points.

HE = Horizontal equivalent; It is the distance between the two given points as measured from the map.

Procedure for gradient determination.

Identify the two points and name them like A and B.

Join the points using a straight line to form line AB.

Measure the ground distance between the two points.

Calculate the actual distance using map scale given to get the horizontal equivalent (HE).

Calculate the difference in height between the two points using the contours.

Using the formula to have the gradient.

Gradient of a slope from point A to B

According to the given case on the map;

Highest altitude = 1,000 m

Lowest altitude = 200 m

CD = 8 cm

Scale; I cm represents 0.5km.

Then;

1,000m – 200m

(8 x 0.5km) x 1,000m 800 = 1

4,000 5

Thus; the gradient is 1 in 5. This implies there is a rise of 1 m high in every horizontal distance of 5m from A to B Or there is a fall of 1 m low in every horizontal distance of 5 m from B to A.

Average Gradient.

Average gradient is a degree of slope steepness for the elongated feature.The elongated feature can be of like a road, river, railway and others of the same nature.

Procedure for average gradient determination.

Identify the two points of the elongated feature.

Measure the length of the elongated feature on the map to get the CD.

Convert the CD into AD b using map scale to get HE.

Calculate the difference in height of the feature using the contours.

Using the formula to have the gradient.

Example:-

The average gradient for the road is determined as follow:-

According to the given case on the map;

Highest altitude = 1,460m

Lowest altitude = 1280m

CD =12cm

Scale; 1cm represents 0.5km.

Then;

1,460m – 1280m

(12 x 0.5km) x 1,000m

1180 = 1

6,000 5

Thus; the average gradient of the road is 1 in 5. This implies; the road experiences a fall or rise of I m low and high respectively in every horizontal distance of 5m in between of points C and D.

Asses your self!

Are you able to define a cross section?

Are you able to describe the kinds of cross section?

Are you able to narrate the significance of drawing a cross section?

Are you able to draw a cross section?

Are able to narrate the factors affecting intervisibility?

Are your able to suggest intervisibility by considering cross section and affecting factors?

Are you to define horizontal equivalent and gradient?

Are you able to calculate gradient and horizontal equivalent.

EXERCISE

Qn. Calculate the gradient between Fotobiro hill and the point at grid reference 040640 (necta 2002 – Extract map of Nyakwere).

Qn. On the map drawn on scale of 2cms to 16 kms, there are two towns, A (altitude 800 meters and B altitude 1200 meters).

calculate the gradient of the slope if the distance between the towns measures 4.2 cm the map.

Find the vertical exaggeration of the cross section if the vertical scale is 1:80,000. (NECTA 1997).

Qn. Draw a cross section from Mahenge peak and the western peak of Wibete hill. (NECTA 1993; Extract map of Dodoma West sheet 162 /1).

Qn. The airfield and the top of the hill at Ilboru are 6.6kms apart. Calculate the

gradient between them (NECTA 1992; map extract part of TANZANIA – ARUSHA sheet 55/3).

Qn. Construct a neat annotated cross section from grid reference 630770 to 740770 (NECTA 1980 – the map extract part of TANZANIA – MONGOYO (Series Y742 sheet 295/1 Edition 1 TSD).

Qn. How would you determine the following on a topographical map? Stream gradient.

Vertical exaggeration.

Horizontal equivalent (NECTA – 1983).

Qn. (i) Draw a cross section from Grid 360280 to 460330 and show area with plantation agriculture and the three major rivers.

calculate the vertical exaggeration.

(NECTA 1992 map extract part of TANZANIA – ARUSHA sheet 55/3). Qn. Draw a cross section from point A to B , and calculate the vertical exaggeration (NECTA 1989).

Qn. Determine the average gradient of river Kwamu kwme from grid 234626 to grid 196596. (NECTA –

2001, the map extract of KONDOa (sheet 104/4).

Qn. Calculate the gradient from Gr 000315 to Gr 020320. (NECTA – 1999, the map extract of BABATI (Y.742).

Qn. Calculate the vertical exaggeration for a topographical section across a map whose horizontal scale is one to one km and the subdivision of the vertical scale being one cm representing 50 m. (NECTA 1988).

RELIEF FEATURES IDENTIFICATION ON TOPOGRAPHICAL MAPS

Topographical maps show numerous relief features of areas represented. The relief features are widely shown by means of contours. Usually contours on maps occupy patterns with respect to the shape of the landforms (relief features). The identification of landforms on the topographical map is by looking the patterns of the contours as well as their numbers. This can be aided by drawing a cross section.

Identification of the varied landforms on the topographical maps with respect to their shape is as follows

1.Hill.

Hill is a rounded up land not as high as mountain. Or

As small rounded upland of low height above the surrounding area.

On the topographical map, hill is recognized by the presence of roughly circular contours close together and the last highest contour round small space on the map.

Plateau.

A plateau is an extensive upland with steep slopes and fairly gentle slope or flat on the top surface.

On the topographical map, plateau owning to its nature is recognized up on the presence of roughly circular contours close to one another but, the last highest contour rounds a large space on the map

Ridge.

Ridge is a big, narrow and long with steep slopes. It is recognized if there is the presence circular elongated contours close to one another.

An escarpment.

It is an upland that has gentle slope on one side and steep slope on the other side. On the topographical map, escarpment is recognized if there is the presence of roughly circular contours observed be very close to one another at one part and far part at the other side.

Slope.

Slope is a slanting piece of landscape. Or the ground that progressively falls or rises from one area to another.

There are five types of slopes and include:-

Steep slope.

Gentle slope.

Concave slope.

Convex slope.

Vertical slope.

Steep slope.

Steep slope is the one that has high degree of steepness evenly from the top to the bottom. Steep slope is recognized if on a topographical map, contours lie evenly spaced much close to one another from the top to the bottom.

Gentle slope / regular slope

Gentle slope refers to a kind of slope that has low degree of steepness more evenly from the top to the bottom.

On the topographical map, gentle slope is recognized if contours indicating the presence of slating land, observed to lie far apart evenly spaced from the top to the bottom.

Concave slope.

It is a slanting land, which is steep at the top and gentle at bottom. Or a slope that appears to have high degree of steepness at the top and low degree of steep at bottom. Concave slope is recognized if the contours indicating slanting land, observed to be closely spaced at the top part and wider apart at the bottom.

Convex slope.

It is the slanting land which has low degree of steepness at the top and high degree of steepness at the bottom. The contours of convex slope are close to one another at the bottom and wider apart at the top.

Vertical slope.

It is the slope that has right angle steepness of about 90°. It is recognized if contours of different elevation join and form a single contour line.

Saddle or Col.

A saddle or col is a low lying land in mountain range, which connects two mountain peaks or hill. The contours of a saddle or col that enclose two mountain peaks or hills, run roughly parallel and are far apart at the low lying land.

Pass.

Pass is a gap through a mountain allowing a through passage to different directions. Pass on the map is recognized, if contours of mountain peaks roughly converge towards a low-lying area.

Watershed.

Watershed is a line dividing the headwaters of two or more streams flowing to different directions. On the contoured map, watershed is recognized provided the highest contours run parallel to each other and streams of water appear to diverge to different directions.

rRr    

River valley:-

River valley is a long narrow and deep depression through which a river

flow. On the topographical map river valley, is recognized if the contours form V shape and the river crosses each contour.

figure here

Spur:-

Spur is a projection of land or broad tongue of land from the side of a hill or mountain towards the valley. Spur is recognized if the contours form a V shape pointing down low lying area.

Gorge.

Gorge is a deep, narrow, steeply sided river valley. The contours of a gorge are close together forming a narrow V shape pointing sharply up-stream and the river crosses each contour.

Flood plain

A flood plain is a flat low lying area lies immediately after river channel built up by deposition of alluvium. Flood plain on the map is recognized if the contours run roughly parallel to the main river and the lowest contours are spaced enough in a way that, it marks a general width of the

flood plain.

Delta:-

A delta is a flat low lying area of alluvial deposits at the mouth of the river crossed by many distributaries. On the topographical map, delta is recognized if the lowest contours follow roughly the area with tributaries.

Estuaries:-

An estuary is a single broad river mount where a river enters a lake or sea. The contours of an estuary are widely spaced forming the wide V shape that point up stream.

Cliffs.

A cliff is a high rock face along a coast, river or lake. On the topographical map, cliff may be indicated in two ways.

A cliff may be shaded by short lines drawn at right angles to the coast, river or lake to indicate the steepness of it.

Cliff on the topographical map may also be observed by the presence of contours of different elevations, join and form a single contour line parallel to the sea, lake or river.

Levees:-

Levees are the natural embankments built up by a stream along the edges of its channel. On a topographical map, the embankments are shown by pecked lines at right angle to the course of the river.

Coral fringed coastline.

Coral fringed coastline is formed by a coral platform which lies close to the shore. On a topographical map, the coral fringed coastline is marked clearly by shading or by using symbols to show the area with coral fringing reef in the sea.

Asses your self!

Do you understand the nature of landforms commonly shown on topographical maps?

Are you able to identify different landforms the topographical map by considering the pattern of contours.

EXERCISE:-

Qn. (i) Describe the land forms shown on the map.

Mention two factors which have influenced the direction of tributary into tributary R

Identify the feature at Y. (NECTA – 1988).

Qn. Describe the major landforms depicted on the map. Use the specific examples from the area (NECTA 204, the map extract of Mwanza sheet 33/2).

Qn. What type of landforms are depicted on the map? (NECTA 2008). Qn. What features are found at grid reference,

(i) 960200? (ii)01139?

(NECTA -1993, map extract part of Tanzania-Dodoma west Sheet 162/1).

Qn. Identify the features found in the following grid readings

(I) 690110 (ii) 579145 (iii) 674063 (iv) 553123

(NECTA 2012-Uyole extract map sheet 245/3).

MAP INTERPRETATION

Map interpretation is the art of examining the given topographical map to realize the reliable geographical details of an area represented. Geographical details may include; climate, economic activities, relief, mode of transport etc.

Map interpretation is done by looking the conventional symbols and signs on the map and realize what they stand for. Map interpretation has to entails two basic processes of map reading and map analysis.

Map reading; It is an art of examining the given topographical map to recognize the features that directed on the map.

Map analysis; It is the art of relating the features that appear on the map to other geographical facts which are required to be described, explained or suggested.

In the process of map reading; carefully read and note; the map conventional signs and symbols, key the date of compilation, title, north direction, latitude and longitudes, and other important marginal details. However the perfect skill for interpretation of the topographical maps requires constant practices and wider geographical knowledge.

With map interpretation; some one is able to describe and explain the following geographical

details:-

·    Climate.

·    Human activities.

·    Vegetation.

·    Drainage.

·    Geological nature.

·    Relief.

·    Geomorphologic processes.

·    Communication.

·    Population distribution and settlements.

CLIMATE

Climate is the average (overall) weather conditions experienced in an area especially large area for a long period of time or through out. It is thus; realization and description of climate of an area from the topographic maps is by taking into consideration of the facts much related to climate which commonly shown on the map. They considerably include the following:-

(i) Latitude:-

Climate conditions vary considerably from one latitude region to another. It is thus; if the latitude region in which the mapped area is found observed, map user may realize the more likely climatic conditions of the area with regards to the wider geographical knowledge the person has.

The latitude region is recognized by taking into consideration of the degree numbers indicated along the map edge from bottom to the top or from south to north. Such degree numbers are of latitude values. Therefore; once you are given a topographical map to establish the climate of the respective area, try to observe the latitudes of the mapped are to understand in which geographical position over earth’s surface the mapped area represented is located.

For instance:-

If the mapped area understudy is located from or in between 0° – 5° north and south of the equator, it implies that, the area is located in the equatorial belt.If other considerations remain constant, the area is suggested to experience equatorial climatic pattern with the following conditions:-

High rainfall through out the year with two maxima peaks i.e. there is no prolonged dry season.

High temperature throughout the year with small annual range.

If the map along its edge shows any latitudes in between of 6° – 20° North and south of the equator. It implies the area represented on the map located in tropical region. If other considerations remain constant, the area is judged to experience tropical climatic type with conditions of:

-Moderately high rainfall which varies annually i.e. there is the presence of both wet and dry seasons in a year.

-Temperature is high with great annual range.

However; if the altitude is below 500m; the area can be suggested to

have coastal tropical climate with long rain season; but if altitude is above 500m, the area can be established to have continental (interior) tropical climate.

Note.

It is important for the map users to be aware with the climatic conditions experienced in varied natural regions.

(ii) Altitude.

Altitude means the height of an area from the mean sea level. Altitude has a considerable impact on climate as temperature and rainfall regime is influenced by altitudes. It is therefore, the consideration of altitude of an area from the map, may help to suggest the likely climatic conditions. With respect to this, once you are given a topographical map to suggest climate, consider the altitude of the area by reading the number of contours, spot height, bench mark and trigonometric points to realize whether the area represented on the map is of lowland or high land.

If the altitude is higher mostly above 2000m implies the area represented is of much highland and likely to experience highland climatic pattern featured by high rains of orographical type which may vary with aspect and low annual temperature as greatly lowered by higher altitude.

If the contours and other means show low height numbers, give an impression that, the area is of lowland and likely to experience high temperature.

iii) Water bodies (drainage).

Drainages are very good guides to climate particularly on the relative amount of rainfall. It is so as the

sources of water bodies in any are on the earth’s surface is mostly by the amount of rain fall received.

Presence of the salt lakes, seasonal streams, boreholes, seasonal swamps and widely spaced streams suggest that, the rains in the area are seasonal with long period of dry conditions.

Presence of abundant permanent streams and permanent swamps, suggests heavy rainfall received in the area.

Presence of the sea, suggests maritime (coastal) climate.

Presence of lake particularly that of Victoria reflects lake equatorial type of climate.

iv) Natural vegetation and crops

Natural vegetation and crops shown on the map have reflection to certain climatic conditions and thus; are also good guide to climate.

Natural vegetation

Presence of thick forests on a map and up on the respective area indicates high annual rains.

Woodland vegetation reflects moderate high annual rains.

Scrubs, scattered trees and thickets vegetation reflect seasonal rains.

Crops.

Crops are raised depending on the climatic conditions that favour their growth. Hence; the consideration of crops cultivated, helps to deduce temperature and rainfall conditions of an area observed on the map.

Presence of coffee and tea on the map and up on the area represented, suggests cool wet climate.

Presence of cotton, sisal and cashew nuts suggests moderately high seasonal rainfall and high temperature.

NOTE.

Always the suggestion of climate of an area from the topographical map, students should not rely on a single guiding fact. Consideration should be centered on more than one guiding facts. It is so in a basis that, climate is influenced by a number of varied factors. It is thus; one considered factor, may not give the absolute reality about the climate of an area.

In East Africa from which most of the topographical maps for examination purpose extracted, the following types of climate experienced.

1. Tropical climate.

This is experienced over most of Tanzania exception in dry region of the central Tanzania. The climate is characterized as follows.

High temperature with great annual range and in high plateau temperatures bit lower as result of high altitude.

The amount of rainfall is moderately high and occurs in one season.

2. Sub tropical climate:-

It is the type of climate experienced in high land areas with in the equatorial belt. It is very common in Kilimanjaro, Kenya highlands, Kigezi, Ngara and Karagwe. The sub tropical climate is characterized as follows:-

3. Desert and semi desert climates:-

This type of climate is experienced in areas of central Tanzania, Northern Kenya and North eastern Kenya; and north eastern Uganda. Desert and semi desert climate is characterized as follow;-

Temperatures are high around 27°C with very high annual range.

Annual rainfall is generally low with long dry season.

4. Coastal Tropical climate.

This type of climate experienced along the coast of East Africa and its islands. The climate is very common in Dar es Salaam, Mombasa, Tanga and others coastal areas.

The costal tropical climate is characterized as follows:-

Long heavy rain season.

Temperature is high with great annual range.

5. Lake equatorial climate.

This is experienced around lake Victoria, in Tanzania, Kenya and Uganda. The climate is characterized by the following conditions:-

Moderately high temperatures.

Moderately high rain rainfall.

Important climate description hints.

Produce a statement in connection to what is to be described about climate.

Give the type of climate and its conditions.

Establish the evidences to reinforce your description (suggestion).

For instance:

Qn. Describe the climate of the area.

ANSWER

Climate of the area being the overall weather conditions as observed from the given extract map is described as follows:-

The area is realized to experience equatorial climate featured by high temperatures with small annual range and high rainfall through out the year.

The realization of climate is supported (reinforced) by the following evidences as observed from the map.

The area is of latitude of 2° indicated along the map edge. Also it is of low altitude. Commonly low latitude sustain high temperature being a feature of the recognized climatic pattern.

Cultivation of cocoa reflects high rains which is also a feature of equatorial climate.

EXERCISE

Qn. With precise pieces of evidence propose the climate of the area shown on the map. (NECTA 2004, map extract of Mwanza sheet 33/2).

Qn. Suggest the possible climate of the area. (NECTA 1993, the extract of part of Tanzania (sheet 162/1).

Qn. Giving evidence from the map, suggest the climate of the area. (NECTA 1987, the extracts series Y 742 sheet 55/3 or ARUSHA).

Qn. Using evidence from the map, suggest the possible climate of the area (NECTA 1989).

Qn. Describe and account for the climate of the area (NECTA 1985, the extract part of Tanzania provide (sheet 55/3 series Y 742).

Qn. Comment on the possible climate of the area. (NECTA 2007, Extract map of West Hai).

Qn. Given topographical map of an area what indicators can be considered in deducing the climate of the area (NECTA 1983).

Qn. Describe how the relief and vegetation can help the map reader to depict climate on topographical maps. (NECTA 1997).

VEGETATION

Vegetation refers to a total assemblage of plant cover in an area. Topographical maps show vegetation with reflection to actual areas represented. It is thus; topographical maps may guide map users to realize the vegetation of an area represented.

The forms of vegetation present in East African areas of which commonly shown on topographical maps include the following:-

Forests:- The vegetation of more close trees; or The vegetation largely dominated by dense growth of tall trees with closed leaf cover or canopy. These develop in regions with high annual rains.

Woodland:- The type of vegetation of less closely big trees. These grown in areas with moderately high annual rains.

Thicket :- This type of vegetation is of dense shrubs (closely shrubs) and some scattered big trees. Such vegetation nature commonly found in regions with moderately high seasonal rains.

Scrubs:- The vegetation of less closely shrubs with widely scattered trees. Such vegetation commonly found in areas of annual seasonal rains with long dry season.

Scattered trees:- These are the vegetation of widely spaced trees. These also commonly found in areas of seasonal rainfall.

Planted vegetation:- Theseare more particularly of the cultivated plants (crops) like sisal, tea, coffee, cashew nuts and others.

The appearance of the distinctive vegetation forms on the topographical map is as follows:-

Vegetation on most of the topographical maps and up on the actual areas represented extremely varied in nature and distribution because of the following factors.

Climatic conditions

High annual rains develop forest vegetation featured by the dense growth of trees.

Moderately high annual rains develop woodland vegetation featured by the less closely trees.

Moderately high seasonal rains develop thicket featured by the growth of closely shrubs.

Seasonal rainfall makes occurrence of scrubs and scattered trees.

Relief.

It is considerably the physical appearance of an area. This influences vegetation relatively to soils and drainage as follows:-

Where the landscape is steep as on a map contours observed to lie much closely to one another, drainage is good, but soils can be shallow. This may give to poor coverage of plants.

Where the landscape is almost level as on the map contours observed to lie much more far apart, deep soils develop, but the area subjected to poor drainage. This also may make poor plants growth e.g. areas of seasonal swamps.

Where the landscape is gentle sloped as on the map contours observed to lie far apart, may have deep well drained soil. This may make good coverage of plants.

Soil:-

Soil has ideal influence to plants growth in the following ways:-

Fertile soil by being deep well drained makes good growth of plants. Such soil sustained where the topography is gentle sloped; and on the map can be realized if contours lie less closely to one another.

Poor soil by being shallow, water logged makes poor growth of plants.

Human activities:-

Areas under human utilization like; scattered cultivation and settlements, plants have been removed and thus; subjected to have poor coverage of plants.

It is unlike to areas that not subjected to human utilization, can be observed to have good coverage of plants if other factors are also favorable.

Important vegetation description hits.

To describe vegetation, carefully study the map key to recognize the conventional symbols representing vegetation and relate to map face. After this the following hints can be given.

Identify the types of vegetation shown on the map like, forest, woodland, scrub e.t.c.

Give the distribution of each identified type of vegetation.

Describe the extent of coverage of each identified type of vegetation.

EXERCISE

Qn. Explain the factors that have influenced the distribution of vegetation of the mapped are (NECTA, 2006. The map extract of Mpanda 153/30).

DRAINAGE

Drainage is the removal of surface water from an area by the system of both natural and man made water bodies like of rivers, lakes, swamps, ditches, canals and other related systems. The common drainage systems of areas which normally observed on the topographical maps include the following:-

Swamps:-

A swamp is a body of shallow stagnant water that normally occupies an area of flat low lying land. Swamps normally found where the ground forms a shallow depression or is extensively flat.

Swamps make drainage by receiving water drained into them by the streams of water flow in wet season.

Swamps are of different types and are shown using different symbols. The swamps are explained in the key of topographical map.

The different types of swamps include the following:-

Mangrove swamp:- These on the topographical maps can only be found along the parts of the sea shore. This is because mangroves only grow in salty sea water.

Tree swamps:- These are the water waterlogged areas which have trees and other smaller plants growing in them.

The papyrus swamps:- These are dominated by papyrus plants.

Marshes:- These are dominated by grasses like plants.

A bog:- It is water logged spongy ground with a surface layer of decayed vegetation.

Sea:-

It is a large extensive body of salty water. This makes drainage by receiving water discharged into it by rivers. The sea is usually shaded in stipples (very small dots).

Lakes:-

These are bodies of water that occupy a basin, depression or hollow on the earth’s surface. They make drainage by receiving water drained into them by rivers and form an important inland drainage system areas.

Reservoirs:-

These are the human made lakes which formed when people build dams across streams or rivers.

Ponds:-

A pot is a small area of stagnant water which is commonly found along the stream courses. Most of the ponds are shown on the map using a dark blue tint.

Waterholes:-

A water hole is a shallow broad pit constructed by people. It is meant to trap rain water for animals to drink. It is shown on the map using the initials WH and a small circle which precedes the initials.

i.e. oWH.

Ditches:

These are the trenches constructed in water logged areas for the purpose of draining water from the land. On topographical maps are shown by straight blue lines and the word ditch commonly written along side the line.

Rivers:-

A river is a mass flow of water in a natural channel from the area of upland towards the

area of lowland where is likely to discharge its water.

A river can be permanent or seasonal. Permanent river can be topographical maps shown by irregular blue lines, and if the river is considerably big, the line appears thickened. While; the seasonal rivers are shown by the broken blue irregular lines. It has to bear in our mind that, some places have rivers which disappear as water percolates into the ground. Rivers of this nature on the map shown by continues irregular lines which end abruptly.

Drainage system of rivers occupy patterns depending on how tributaries converge to the main river and the general appearance of both consequent and subsequent streams. Drainage pattern is thus; defined as a layout made by the rivers on the landscape or is the shape produced by the arrangement of tributaries and main-river in a catchment area.

The patterns of rivers is the result of certain determinant factors which include the following.

1. Slope of the land.

2. The nature of the underlying rocks.

3. The general relief pattern of an area.

The common river patterns of areas appearing on topographical maps include the following:-

Dendritic pattern:- It a drainage pattern in a shape of a tree trunk like structure with tributaries converged to the main river at acute angle resembling the shape of a tree like a feature. It develops on landscape of uniform rock hardness and structure and on gentle slope landscapes. It is very common in areas of igneous rocks.

Trellis or rectangular drainage pattern.

It is a pattern which occupies a shape of a lattice with tributaries converging to the main river at almost right angle. It develops on a catchment’s area whose landscape has variation in rock hardness and structure. It may also occurs in areas of faulted landscape.

Radial pattern:-

It is a drainage pattern whose tributaries diverge outwards down from the summit of rounded highland to different directions forming a shape of spokes round a wheel like structure. It is common to areas of roughly circular hills of igneous rock.

(iv) Centripetal pattern:

It is the one whose tributaries flow from different directions converging at a center of down warped landscape, where there is a swamp or lake. It is largely controlled by the shape of the landscape

River course (stage) identification

It has also to be noted that, a river has its course if development marked with three stages of life cycle. The stage of a river on a topographical map can be identified as follows:-

Youthful stage.

It can be easily identified by the presence of the following;

The narrow V – shape contours like arrow heads pointing up to highest ground.

Very close contours along the river course, which represent steep valley sides.

Lack of meanders.

Absence of a flood plan.

Very few tributaries.

Mature stage:-

It is recognized by the following facts on the map.

Contours have a U – pattern crossing the river at wide interval which represent more gentle gradient.

The landscape is fairly flat with a narrow flood plan on either side of the river.

Presence of many tributaries.

Low degree of meanders.

Old stage.

It is observed by the following facts.

The presence of a very gentle gradient of the river course.

Contours are very far apart cross the river.

More pronounced meanders.

The presence of a river broad flood plain.

Factors influencing drainage systems.

Drainage systems observed on topographical maps with reflection to actual areas represented are the result of the following determinant factors:-

Climate.

Occurrence of rainfall, supply water to surface which then development to water body systems of rivers, swamps and others as follows:-

Heavy and continues rains, make areas to have permanent rivers and permanent swamps.

Seasonal rains make areas to have seasonal rivers and seasonal swamps.

The nature of underlying rocks:-

Impermeable underlying rocks influence the occurrence of swamps. This moreover makes rivers to flow steadily regular as water is in difficult to percolate into the ground.

Permeable rocks make rivers to flow irregularly as may end abruptly.

Rocks of uniform hardness influence rivers to develop either dendritic, radial and parallel patterns if other factors remain constant.

Relief / topography.

Sloped topography develop rivers as water make flow from the areas of upland towards the areas of low land.

The extensive flat low lying topography influences the occurrence of swamps as bodies of shallow stagnant water occupying flat low lying areas.

Depressed topography encourages the occurrence of lakes. Moreover, may influence the occurrence of centripetal pattern.

The conical shaped uplands encourage the occurrence of radial drainage pattern.

Important drainage description hints.

When describing drainage of an area from the given topographical map, the following if possible as important hints should be given.

Given the statement in connection to what you need to describe about the drainage of the area from the map.

Identify the main features of drainage in the area as observed from the map. These may include; swamps, rivers, lakes, etc.

Give the location of each feature on the map with reflection to the actual area represented.

Give the characteristics of the identified drainage features like coverage, patterns, direction, seasonality, etc.

For instance:

Qn. Describe the drainage of the area.

ANSWER

Drainage refers to the removal of the surface water from an area by the layout of water bodies.

Therefore, the drainage of the area as observed from the given topographical map is described as follows. The area is drainage systems of river, swamps, and lake.

Rivers; these are the flow of water in definite channels. They largely drain the area particularly the northern part where the landscape is comparatively higher and most of the rivers start to flow towards the southern part where the landscape is comparatively low. The rivers observed to occupy dendritic pattern. Some of the pronounced rivers include of Malela, Kitungwe, Kitogota, Lusingo, Kuga, Mbingu and others which might be present in the area.

Swamps; These are the bodies of stagnant water which are observed to occupy flat low lying lands and in are all seasonal. These observed in the southern part of the area where the landscape with observation to contours is almost level. Swamps in the area make drainage by receiving surface water drained into from rivers.

Lakes; These also make considerable drainage in the area. These observed in south east part where the landscape depressed. The most remarkable lake is that of Mnyamani and make drainage by receiving water discharged into it by rivers.

EXERCISE

Qn. Explain how the drainage pattern of the area is related is related to relief (NECTA, 1993 …..THE MAP EXTRACT PART OF Tanzania – Dodoma west (sheet 162/1).

Qn. Comment on the drainage pattern of the area. (NECTA 1995 – the map extract of part of Tanzania –

KILWA KIVINJE (sheet 256/2).

Qn. Explain the main factors which have influenced the drainage system of the area. (NECTA 2000, the extract Madukani series Y742).

Qn. Describe the drainage pattern of the area. (NECTA 1987 the map extract part of Tanzania provided (sheet 55/3 series Y72.)

Qn. Comment on the drainage in the area. (NECTA, 1985 the map extract part of Tanzania provided (sheet 55 series Y742).

Qn. Explain the relationship between relief and drainage of West Hai. (NECTA 2007, the map of WET HI, (sheet 56/1).

Qn. Explain how drainage pattern of the area is related to relief (NECTA 1991, the map extract of part of TANZANIA Fig.1).

ROCKS NATURE

Rocks are the aggregate or mixture of materials in solid form contented with minerals. Rocks are extremely varied and popularly include; igneous, sedimentary and metamorphic rocks.

The rocks of an area in exception of the out crop rocks and coral reefs are not directly shown on topographical maps. Rock nature can be identified by taking into consideration of the geographical facts related to geology which commonly shown on maps. These include the following:-

Landforms:-

Land forms are good guide to rock nature identification of an area from a topographical map.

The presence of volcanic landforms on the map.

Like crater, caldera, conical hills and mountains and others, reveals the igneous rocks of both intrusive and extrusive.

The presence of coral reef reveals the organically formed sedimentary rocks.

The presence of depression, sand dunes, and beaches reveals existence of less resistant rocks of which easily worn out into residuals to form such landforms by accumulation.

Drainage features:-

Drainage features in areas strongly related to the nature of geology. It is thus; consideration of the drainage features may helps to realize the existing geological nature:-

The presence of dendritic, parallel and radial drainage patterns reveals the presence of hard rocks. Commonly such river patters develop on landscape of uniform hard rocks.

The presence of swamps and lake reveals the existence of impermeable underlying rocks which limit the percolation of water into the ground.

Vegetation:-

Certain vegetation much related to geological nature of areas. Therefore; the consideration of vegetation may help to suggest the nature of rock of an area.

The presence of thick forest; and crops of coffee and tea suggest the existence of igneous rocks. It is so as such plants found where the soil is fertile. In consideration, most of fertile soils are derived from volcanic igneous rocks.

The presence of poor vegetation suggests the existence of sedimentary rocks as such rocks have low ability to retain water for plants.

Note:-

Metamorphic rocks have poor indicators (evidence). Probably, the presence of poor vegetation may reveal the existence of such rocks.

RELIEF

Relief refers to the physical appearance (surface form) of an area by landforms of contrasting shape and size.

The realization and description of relief of any area from a topographical map is by observing the patterns of contours and their respective heights. The arrangement (pattern) of contours reflects the surface form physical appearance), while the numbers reflect the altitudes.

In common, the relief of the area can be of either highland or low land. The area is recognized to be of high land if is of high altitude above 500m from the mean sea level. Lowland is recognized if the area has low altitude of below 500m from the mean sea level.

RELIEF PATTERNS OF AREAS.

The common relief patterns recognized from the topographical maps and up on the areas represented include the following.

Mountain landscape:-

Mountain landscape is a surface form that rises more steeply or abruptly to summits above the surrounding area over wider area. On a topographical map mountain landscape is recognized, if contours lie so much closely to one another over a considerable wider part. Moreover; the map by

contours shows many hills or summits, dissection of rivers (streams), the presence of passes, saddle, water shed and escarpments.

Plateau landscape:-

It is an extensive highland area, generally, level or gentle sloped at summit. On a topographical map is recognized if the landscape is assessed be of high altitude and wider part is almost level or gentle sloped. Thus; the contours observed to show higher height numbers and lie far apart to reveal a general level, and might be dissected by rivers.

Hilly landscape:-

It is an area predominated by numerous isolated hills. On a topographical map is recognized if the contours or roughly round close to one another appear numerous and isolated.

Coastal plain:-

It is an extensive area of low altitude lies immediately after the sea. The lowland Coastal plain is recognized if contours on the map are widely spaced and the elevation rarely exceed above 300m.

Beside to this, the mapped area is observed to lie immediately after the sea.

River basin:-

The lowland of a river valley is recognized if the mapped area is observed to lie parallel to the big river and the contours show low height numbers.

Important relief description hints.

Generally, in making description about the relief of the mapped area, the following hints should be followed.

The map has to be divided into relief regions. This is done by observing contrasting contour arrangements.

Give the position location of each relief region as shown on the topographical map.

Give the general description of each relief region by giving out the prominent landforms and altitudes of each region.

EXERCISE

Qn. Describe the relief of the mapped area. (NECTA 2002, the map of part of KENYA – NYAKWERE).

Qn. Describe the relief of the area shown. (NECTA 1996, the map extract Y742 55/3 or ARUSHA (reproduced from the same series).

Qn. What type of landscape does the map depict?

(NECTA 1995, map extract of part of Tanzania – KILWA KIVINJE (sheet

256/2).

Qn. With specific evidences on the map, suggest the landscape patterns that predominate in the area.

(NECTA 2003, the map extract of SONGEA sheet 299/1).

GEOMORPHOLOGIC PROCESSES.

Geomorphologic processes refer to the natural activities (physical processes) which mould an area by resulting into the occurrence of landforms. Geomorphologic processes moulded the area from the topographical map, realized and suggested by taking into consideration of the following.

Land forms.

The presence of volcanic land forms such as craters, caldera and volcanic hills and mountain reflects vulcanicity.

Presence of block Mountains reflects crustal uplift by earth’s movement.

The presence of escarpment reflects both faulting and denudation.

Presence of sand dunes, delta, beach, flood plains and levees reflects deposition.

Drainage.

Presence of rivers and lakes suggests erosion and deposition provided the formed related features observed on the map.

Presence of oceans reflects marine erosion and deposition provided the related features such as cliff and beach respectively observed on the map.

COMMUNICATION.

Communication in most of areas is enhanced by the means of transport and

telephone networks. Hence on topographical maps communication is recognized up on the presence of the means of transport, telephone lines and telephone towers.

FORMS OF TRANSPORT

The topographical maps may show one or more forms of transport with reflection to areas represented. These include the following.

Land transport;-

This form of transport is by road, tracks, railway lines and foot path.

Roads:- These are of the varied nature and include the following:-

All weather road bound surface. They are tarmac roads and normally used throughout the year including during the rainy season.

All weather road loose surface; they are murram surface road and also used throughout the year.

Dry weather road; These are also murram surface roads, but

Footpath:-

These are the ways through which people move from one area to another on foot.

Rail transport;

It is reflected by the presence of railways; and these may appear on the

topographical map provided the represented area is served by this particular means of transport, or the railway line pass through the area.

Railway lines as observed from the topographical maps with reflection to areas represented, are of two categories and include the following.

Main railway lines; These on the topographical maps represented by the black shading which alternate with white ones.

Light railway lines: These are normally present with in plantation and mining areas. These are represented by the thin black lines which may be pecked.

Air transport

Air transport about areas can be realized if the following observed on the topographical maps

Air port. This is a large area on the ground which is used by commercial airlines to land or to take off. It has facilities for passengers, goods and offices including of immigration.

Aerodrome. This is small airport that is mainly used by private air craft.

Airfield. This is area of open and level ground where aircraft may land or take off. These normally have offices for air craft operations. However; the offices are not as large those of air ports. Airfield runway can be bound , murram or grass

Water transport:-

Water transport on the topographical map with reflection to the area represented is revealed by the presence of ports, big lake, sea and ferry across the river, lake or part of the sea; wharf, berth, jetty and pier.

Wharf is a wooden or stone structure that is constructed at the water front onto which boats or ships are tied when they are being loaded or off loaded.

A berth is the space on the side of the wharf which is set aside for a ship to anchor.

A jetty is a structure that is built out into the water for breaking the waves. This keeps the water calm on the side of the land. It may have also serve as a landing place.

A pier is a structure which is made of wood, iron or stone. It is built out into the lake or sea for walking on and for ships to stop and load or unload. Pier is bigger than jet and may have restaurant on it.

FACTORS INFLUENCING TRANSPOTATION.

It has to be noted that; types, layout and quality of the means of transport as observed on maps with reflection to the actual areas represented influenced by the following factors.

1. Relief.

Relief being the physical appearance of an area influences both; layout and types of transport as follow.

Roads and railways avoid to pass through areas of steep slope and are more liable to pass through areas of gentle slope. Thus; the layout of the overland transportation is observed in areas of gentle slope as such areas are less expensive for construction and also less hazardous.

However, roads have more advantage than railway in this respect as motor vehicles can travel more easily uphill than trains.

2. Drainage.

Roads and railways avoid to pass through areas with many rivers and very flat areas liable to floods. It is hazardous more expensive to establish means of transport through areas of this nature.

3. Economic activities.

Means of transport are made to pass through the areas where economic activities are carried out to facilitate the carriage of the economic goods.

4. Settlements

The layout of roads and railways is observed in areas where human settlements exist to facilitate the movement of people as well as their goods.

In urban areas; air transport observed and other means transport of high quality. It is unlike to rural areas.

Important transportation description hints.

To interpret communication, some one has to study carefully the map key to detect the convention signs representing means of transport and relate them to a map face and the following hints can be given.

Give the statement in connection to what you are going to describe about the area from the map.

Identify the main means of transport in the area as observed from the map. These may include; land transport, air transport and water transport.

Give the characteristics of the identified means of transport like; layout, quality and others.

EXERCISE

Qn. With reference to the relief and settlement pattern of the area, account for the type, lay out and quality of over land transportation. (NECTA 2006, the map extract of Mpanda sheet 153/3)

Qn. Describe the nature of transport as seen on the map (NECTA, 1997 – the map extract of MOSHI series Y742).

Qn. Explain the communication of the area and show they are influenced by physical features. Comment on how the communication might be developed to meet future needs. (NECTA 1980, the map of TANZANIA – MINGOYO Serial Y742 sheet 295/1 Edition 1 TSD 1967).

Qn. Relate settlement distribution and communication lines to relief and drainage. (NECTA 1985, the map extract part of Tanzania provided (sheet 55/3 series Y742).

Qn. Comment on the transportation system of the area 56/1.