Maps and map interpretation

CONTENT OF MAPS

Map content refers to a body of information inserted on a map with reflection to the actual area represented. i.e. the details shown on a map which reflect the nature of the area represented or what generally contained on the map.’

The content established on topographical maps are so varied and thus ; classified into three categories of the following:-

Natural contents:-The features which are distinctive from man made. They include: relief features, drainage features, vegetation features and others.

Artificial contents: These are considerably to the features of man made such as cemetery, roads, railways, settlements, airfield and others of the same reflection.

Supportive contents: These are the marginal details established to make well defined. Some of the supportive details include: scale, heading, key, date of compilation, northern direction and others of the same reflection.

FACTORS WHICH DETERMINE CONTENT OF MAPS

Most of the maps do not show (have) similar content i.e. details are considerably varied from map to maps. For instance: a map of Africa observed to show political boundaries of the countries, while the other shown physical appearance of the continent. Moreover: a map may appers more detailed; while the concluded that, variation of details on maps occurs as functioned by certain of details on maps occurs as include the following:-

1. Objectivity of the map drawn

2. Scale size of the map used

3. Date of compilation

4. The nature of the area represented

5. The nationality of the cartographer

1. Objective of the map drawn

This largely depends on the aim of the cartographer (map maker). Usually maps are selective as it is difficult for all surface details to appear the map. Hence any map reflects its purpose.

2. Scale size of a map used

Maps are drawn on varied scale size depending on the size of the ground and size of the map it self. It has to be taken into consideration that, scale size of a map is what determines the amount of details of an area to be shown on the map, in common, a map drawn on a small scale is made to have limited space and less details would have been shown on it. Conversely to a map drawn on large scale , is made to have large space and very possible to display a lot about the represented area.

3. Date of compilation

Date of compilation refers to a period of time when a map was designed. It has to be taken into consideration that, land details are dynamic over time. With respect to this, a map is likely to show details which were present by the time of its designation. It is likely to have variation in details.

4. The nature of the represented area

A map shows what is found in the represented area and not otherwise. Therefore, maps which details.It is thus, a map reflects the reality of the area represented.

5. Nationality of the cartographer.

A map to represent part of the earth’s surface can be constructed by the foreigner or local cartographer. The two maps may differ in content due to the fact that, the foreigner cartographer might not to include some surface details because of being not familiar with the area. Moreover the foreigner cartographer may misname the places on the map of the region represented.

EXERCISE

Qn. (a) What factors affect the content of topographical map?

(b) Classify the features that are commonly shown on topographical maps. (NECTA 1991)

Qn. Explain the factors that affect that affect the content of topographical maps. (NECTA 2008)

CARTOGRAPHY

Cartography is an art or a science of designing a map to represent either the whole or any part of the earth’s surface in scaled and conventional form.

There are noticeable contrasts between maps and the whole or parts of the earth’s surface represented as follow:-

1. Map is flat, while the earth’s surface or part of the earth’s surface is not flat.

2. Maps are much smaller in size, while the whole earth or a part of the earth represented is much larger in size.

3. With this the map makers use a cartographic technique to maintain the accuracy of the earth’s shape and size on maps. The technique is known as map projection. It is thus; the cartographic technique is associated with map projection. It is thus; the cartographic technique is associated with map projection as a sole means of maintaining accuracy of areas on maps.

MAP PROJECTION

The earth’s surface can be wholly represented with reasonable accuracy on a globe. But globes are not as convenient as flat maps to use. Globe can not depicts much details like transportation system of a city, or the location of very small towns or villages. With this, maps have to be produced to facilitate geographical studies.

To make the maps so accurate, a cartographic technique of map projection is defined as the cartographic technique of transforming the shape of the earth’s surface or part of the earth’s surface more accurately to a plane surface to develop a map that can be easily worked with less distortion.

i.e. It is the cartographic technique of maintaining the accuracy of an area on a map.

The cartographic technique of map projection is recognized be of varied types as flat bodies into which maps developed differently projected. This develops cylindrical, conical and plane map projections

The cartographic technique of map projection is recognized be of varied types as flat bodies onto which maps developed differently projected. This develops cylindrical,conical and plane map projections. More over;on a map, the features are made to have accuracy on different respects. This also develops the types of azimuthal, gnomic and stereo graphic map projections.

Cylindrical projection

By cylindrical projection, the shape of the earth’s surface is accurately maintained as a frat body onto which a map would be drawn, projected to a shape of the earth’s surface is maintained and then the cylindrical projected body is cut to develop flat map onto which the whole earth surface appears.

Cylindrical projection is alternatively known as mercators projection.

Conical projection

It is a considerable form of map projection, by which, the shape of the earth’s surface is accurately maintained as a flat body onto which a map would be drawn is projected to a conical shape. Over the surface of projected conical body, the shape of the earth’s surface is maintained then the conical body is cut to develop a flat map onto which the whole earth’s surface or part of the earth surface appears.

Plane projection

By plane projection, the area particularly of a limited size whose accuracy is directly maintained on a flat body os a piece of paper.

Azimuthal projection

It is a type of map projection which mostly used to maintain the correct distribution of the surface features on a map by being maintained in true directons and distance relatively to one another with

reference from the centre of a map and up on the actual area on the earth’s surface. By this, all bearings are laid off correctly from the central point of the map, so that all points on the map and up on the area on the earth’s surface are true in distance and direction from the centre.

Gnomic projection

It is alternatively known as equi-distance projection. This is used to maintain the accuracy of ground distances on the map with respect to the used scale by regarding the relative bearing of the features in the area.

Streographic projection

It is a cartographic technique of preserving the correct shape of earth’s surface features on a map. Preservation of the features is maintained by taking into consideration of the satellite images and aerial photographs.

FACTORS INFLUENCING CARTOGRAPHIC PROCESS (KEY ISSUE CONSIDERED IN MAP MAKING)

In a process of map making a present a certain part of the earth’s surface, the following should be taken into consideration as guides to map maker.

1. The size of the actual area to be represented on a map. The size of the area is revealed by making survey or by examining the vertical photograph that represents the same area.

2.Size of the plane surface of a piece of paper onto which a map would be designed.

3. Map scale. The scale is determined by relating the corresponding distance between the map and ground. Scale is what determines the amount of details about the area appear on the a map.

4. Methods of projection as means of maintaining the accuracy of the map.

5. Nature and amount of the features to be shown on a map. This largely depends on a type of map would be designed under plan and chosen scale size.

PROCEDURE IN MAP MAKING

The construction of a map involves the following important steps:-

the cartographer has to make overall plan of a kind of map to be designed. The plan depends on what is intended to appear on the map about the area. i.e. the plan can be design : topographical map[, statistical map, thematic map or cadastral map.

Collection of data from the area to be mapped. The nature of data to be collected depends on a type of map to be prepared. For instance; if the plan is to prepare a topographical map, the cartographer would have to collect the general geographical details of both natural and artificial features present in the area.

Data can be collected by involving the following methods.

i. Making of the field survey in the area.

ii. By examining the respective vertical aerial photographs.

iii. By examining the respective satellite images.

Data can be delivered from the existing sources like books and other maps.

Choice of a scale. This has to take into consideration of both, size of the flat body of a sheet of paper and the size of the ground to be mapped. The scale is determined by relating the corresponding measurements on distance between the map and ground.

Representation of the data or details on the map. The data can be represented by means of the conventional symbols, varied colours, varied shade textures, writing the names of features or places and other important means.

the map should be given with the supportive details to make it well defined. These include; title, key, north directions, scale, date of compilation and others of the same importance.

LIMITATIONS IN MAP MAKING.

Determination of the map scale; by relating the corresponding distances between the map and ground. The uses scale might have been assessed by using wrong measurements between the map and ground. For instance; the surveyed ground distance to be related to map distance might have been subjected to errors accumulation.

Difficulties in cartographic representation.

It is much based to the representation of the features on a map. The problem a rise on the following.

1. What to be shown on a map regarding that, a map is selective in nature. i.e. It is more difficult to make all details appear on a map.

Representation of the data of the map by inserting the name of the features, conventional signs and symbols, colors and shades. All these require high skill.

2. Dynamism problem. Areas mapped subjected to changes. This makes maps appear outdated. Moreover; it becomes much difficult to update the map.

3. It becomes much difficult for all features maintained on a constant scale of the map.

4. Human problems

5. Technology

The designing of maps requires higher technology. This makes most of the maps designed manually and become not exactly accurate.

6. Financial problems

The making of a map is a expensive process. This makes maps not recurrently produced.

7. Poor communication

This greatly hinders the process of data collection in areas that would be mapped.

EXERCISE

QN. Write briefs notes on map projection (DSM – Mock 2003)

QN. Differentiate between thematic and topographical maps.

Outline the problems encountered in a process of map making. MOCK – Qn.)

ESSENTIAL OF MAP

These are the supportive details given on a map to make it well defined with reflection to an actual area on the earth’s surface represented. Such details make the map well understood and interpreted to recognize clearly the geographical facts of the area represented. The are usually given on the map border. Absence of these on the map, makes difficulties in map reading and interpretation.

The main essentials of maps include the following.

Title

It is a heading of a map designed. The significance of it is to tell what the map is for about. This is commonly indicated at the top of the map; and on other maps appear at bottom.

Map title is of two forms depending on what the map shows and include:- General title

It is given to a map that shows the general geographical details of an area represented. It is established by writing only the name of a region represented. This form of title commonly appears on a topographical map. E.g. MOROGORO.

Specific title,

This is made to appear on a map that shows specific content among of the several about the represented area. Specific title mostly appears on thematic and statistical maps. E.g. MOROGORO LAND TRANSPORT LAYOUT.

Key

It is the list of all conventional symbol, signs and abbreviations together with their meaning on the map border. Maps are conventional in nature as represent land features by means of conventional symbols, signs and initials or abbreviations. It is therefore significantly potential, in order to make a map well defined and understood, it should be established with a key to show what the conventionas symbols, signs and abbreviations or initials stand for.

Scale

A map is much smaller in size compared to the actual area represented which is much larger in size. It is thus, maps are accurately designed up on scales.

It is therefore important for the used to appear on a map in such a way map user may take into consideration of it for futher assessment.

Scale on a map enables the users to understand the relation ship of distance to ground, which then helps to understand the bigness of the area represented and other ground measurements of interest like distance and gradient.

Scale on the map is expressed in three varied ways and these include:-

In representative fraction. E.g. 1;50,000

In statement (verbal expression) eg, 1 cm on a map represents 2kms on the ground.

Graphically; e.g.

Indication of north direction

Any map should be indicate with north direction. On topographical map is commonly indicated by the following conventional sign.

The significance of north direction indication on a map is to enable the map uses to recognize readily the north direction and other important directions of like; North west, East, North east etc, of the represented area. Beside to this; the indicated north helps and features on the map and up on the respective area represented on the earth’s surface.

It has to bear in mind that, bearing of an observation line between two points is measured clockwise from north direction of 000⁰

Margins

It is the frame work of the map designed. The role of a margin is to show the end of the represented area; and also makes the map impressive and attractive to the users.

Date of compilation.

It is a date of map publication. It is very important for a date of compilation to appear on map. The enables the users to realize the following:-

Whether the map is updating or outdated relatively to the actual appearance of the respective area represented.

The changes which have occurred in the area. This can be realized by comparing the latest map to other maps or the given map to the current appearance of the area.

To calculate magnetic variation of a place by taking into consideration of the rate of changes per annum. Be side to this, it may also help to calculate the new magnetic bearing of an observation line from a place to another place.

Grid lines and latitudes and longitudes.

Grid lines are the vertical and horizontal lines drawn on a map face crossing at right angles giving so perfect squares. The lines are numbered to make eastings and northing.

Latitudes and longitudes are the imaginary angular distance lines drawn on the face of map and given with the degree numbers as have been measured more accurately from the centre of the earth’s surface. These represent the angular distance of the area on the earth’s surface from the centre.

Grid lines, latitudes and longitudes in general, have a potential significance of enabling people using map to locate position of geographical features on the map with reflection to actual areas represented.

Moreover; the latitudes and longitudes enable map mapped areas from the centre of the earth. Note.

The grid lines are commonly established in more details on large scaled maps as they represent small areas. While, the latitudes and longitudes are widely printed on small scaled maps as they represent wider parts of the earth’s surface.

Map identification details.

These included both; serial number and sheet number of the map. The are potentially significant in recognizing easily the maps and also make clear distinction map to maps.

Publisher and copy writer owner.

It is important that, to any map the name of the cartographer or institution constructed the map has to appear. This may help the map users to make necessary consultation with the cartographer or institution constructed the map has to appear. This may help the map users to make necessary consultation with the cartographer or institution to have more clear details about the area which has been mapped.