Topic 6: Map Work - TZ notes book
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Topic 6: Map Work

MAP WORK


The Concept of a Map

Define the concept of a map

A map is a representation of an area of the earth’s surface on a flat surface such as paper, wood, board, card, plastic, cloth or some other material.

The information given in a map is shown by conventional signs and symbols which are interpreted by the use of the ―key‖. A map shows important natural and man-made features. Some maps show distributions like rainfall, temperature, air pressure and population. On a map, lines of longitude and latitude are marked to show the position of different areas.

Types of maps

There are many different types of maps, which are generally classifies according to the features they represent. Most of these maps are grouped into two major types:

  1. Topographic maps

  2. Statistical or distribution maps


Topographic maps

Topographic maps are maps that are used to show selected physical and human features of a given area. These maps show:

Location:The geographic location in a map may be shown using:

  1. compass bearing;

  2. grid reference;

  3. latitudes and longitudes;

  4. political and administrative boundaries; or

  5. use of place names.


Landscape: Some of the landscape features shown on a topographic map are mountains, hills, plains, lakes, rivers and shape of coastlines. Relief maps show distribution of relief features such as hills, mountains, valleys and depressions.

Cultural features: Some of the cultural features or artificial features are roads, railways, cities, towns, dams and other structures built by man.

Uses of topographic maps

  1. Topographic maps are useful for describing features of the earth’s surface.

  2. They are used to show the direction. People use maps to reach their destination. That is, they show which direction to go and how far to go.

  3. Town planners use maps to plan the best use of land.

  4. Road builders use maps to design new roads.

  5. Farmers use maps to plan the best use of their farmlands.

  6. Maps are essential to any field of study.

  7. They provide much information on the nature and distribution of geographical phenomena e.g. settlement, population distribution, etc.


Statistical or distribution maps

These maps show such geographical phenomena as distribution of rainfall, temperature, pressure, vegetation, crops, minerals and many other phenomena. The commonly used statistical or distribution maps are Atlas maps. Atlas maps are usually drawn to scale. They represent a large area of the ground on a small space of paper. Maps of this nature are used to show various geographical aspects:

  1. Population maps show distribution of people and settlements e.g. towns and cities.

  2. Vegetation maps show the distribution of vegetation, e.g. forests, bushes and grasslands.

  3. Political maps show political administrative divisions e.g. countries, regions provinces and districts.

  4. Climatic maps show information on elements of climate such as rainfall, temperature and winds.

  5. Economic maps show the distribution of various human activities, e.g. farming, tourism, transport and mining.

  6. Travel maps show the location of places and distribution of hotels, camping sites, historical sites and other interesting places.


Characteristics of atlas maps

  1. They are drawn to scale.

  2. They show whole countries, continents or even the world on a single sheet of paper or page.

  3. They show generalized information. They do not include or show a great amount of detail as shown in topographic maps.

  4. Atlas maps may include and show the distribution of many features such as crops, minerals, roads, railways, towns, relief, vegetation and many others. Such details may be shown by the use of colours, signs and symbols.

  5. Atlas maps are simple and easy to read and interpret. They are easy to draw or to reproduce.


Uses of statistical and distribution maps

  1. They are useful for describing the distribution of many features found on the earth’s


surface or showing certain selected features such as physical, political, historical or economic features.

  1. They are useful for showing generalized information on large or small areas. The following are examples of the uses of statistical or distribution maps:

  2. Physical maps show the arrangement or distribution of mountains, hills, highlands, lowlands, rivers and so forth. (b) Political maps shown areas with their political and administrative boundaries.

  3. Climatic maps show the distribution of temperatures, rainfall, pressure, winds, climatic regions, etc.

  4. Historical maps show the distribution of historical places e.g. historical sites.

  5. Economic maps show the distribution of chief crops, animals, industries, roads, mines,


etc.

Components of a Map

Components of a Map

List all the components of a map

These are basic prerequisites or qualities that any map should have. A map should have:

 

  1. a title, which tells what the map is about;

  2. a key which is used to interpret the signs and symbols found on a map;

  3. a margin which bounds the map;

  4. an indication of the north direction; and

  5. a scale for showing the relationship between the distance on the map and that on the ground.


Each of these components is discussed in detail below:

  • Title:The title shows the topic or subject matter of the map. It gives the name of the area which the map represents or the features represented on that map. The name of the map enables the user to read and interpret the map easily.

  • Key:A key is a list of symbols and signs with their meanings as used in the map. It appears in a box at one of the bottom comers of the map. When these symbols and signs are given in the key, it becomes easier to interpret a map and get accurate information from it.

  • North direction:This is a sign which shows the north direction. The sign gives an indication of the direction towards the north. It is from this direction that other cardinal points and positional locations of different areas on a map can be identified.

  • Margin:This is a frame which encloses the area covered by the map. The margin is useful in that it guides and limits the map users as they read maps.

  • Scale:The scale of the map indicates the ratio between the map and ground distances. It enables the map readers to make accurate estimation of distances on the map as they would be measured on the ground.


A Scale and Different Ways Used in Representing a Scale

Define scale and identify different ways used in representing a scale

A scale is a ratio between the distance on the map and the true distance on the earth’s surface.



Maps drawn to scale show the exact proportionality between the distance on the ground and that on the map.

 

Map scales are very crucial because they enable the map readers to calculate actual distances and areas on the ground based on the scales shown on maps. It is not possible to estimate the actual distance between two points on a map or a particular area on a map without the use of the scale. Though every map should have the scale, sketch maps are usually not drawn to scale. Sketch maps are rough sketches drawn on a flat surface to represent a particular area on the ground.

 

Types of scales

 

 

Map scales are classified on two bases. They are classified based on:

 

  1. the way they are expressed; and


 

  1. their size.


 

Classification of scales based on the way they are expressed based on this mode, map scales may be expressed in any of the following ways:

 

  1. As a statement


 

  1. As a representative fraction


 

  1. As a linear scale


 

Statement scale

 

This is the map scale stated in words or it is a verbal scale. The scale may be stated as ―one centimetre represents ten kilometres or 1 centimetre to 10 kilometres or 1 cm to 10 km.‖

 

It should be noted that in all statement scales map distances are stated in centimetres and ground distances in kilometres.For example it is wrong to state‖ one centimetre represents five hundred metres. The correct statement is ―one centimetre represents a half kilometre.‖

 

Properties of statement scales

  1. They are expressed as word or verbal statements

  2. The scales bear specific units of measurement. Usually the units representing map distances are smaller than the actual ground distances, e.g. 1 cm represents 5 kilometres.

  3. The word ―represent‖ and ―not equal to‖ or ―equivalent to‖ is used when expressing statement scales. For instance, do not state ―one centimetre is equal to one kilometre‖. This


statement is wrong because one centimetre on a map is not exactly equal to one kilometre on the ground but just a scaled representative of the stated distance. The distance on the map is just taken as a representative of but not equal to the distance on the ground. The statement above is correctly stated as ―one centimetre represents one kilometre‖.

 

  1. The map distance always carries the digit 1 while that of the ground may be less than or equal to 1. For example 1 cm represents ? km, 1 cm represents 1 km.


Representative fraction (RF) scale

This is a type of scale which expresses the map distance as a fraction of the actual distance on the ground, for example, 1:10000 or 1/10000. This means that one unit on the map represents 10000 units on the ground.

Properties of RF scales

  1. The scales are either expressed as a ratio or fraction and do not bear any units. The units may be deduced from the linear or statement scale shown on the map.

  2. The top number (numerator) stands for the map distance and is always reduced to 1.

  3. The bottom number (denominator) stands for the ground distance and is usually more than 1.


It is important to note that when assigning units of measurement to RF scales, both the numerator and the denominator should bear the same units, e.g. 1 cm: 100 cm. The units used in most scales are centimetres. So, in case the units are not given, assume the units are in centimetres.

Example 1

Consider a map with an RF scale of 1/10000 or 1:100000. A river on this particular map measures 5 cm. Calculate the actual ground length of the river. Solution

Since 1 cm on the ground represents 100000 cm on the ground, then 5 cm will represent 5?100,000 cm = 500,000 cm . But 1 km = 100,000 cm. then, the actual ground distance is 500,000/100,000 = 5km.

Linear (graph) scale

A linear scale or line scale or graph scale is a line showing the distance on the map that represents a given distance on the ground. It is expressed as a short or long line sub-divided into smaller, equal units. The linear scale is commonly placed at the bottom of the map. There are two categories of linear scales: the short-line scale and the long-line scale.

A short line scale consists of a single, short line that represents the actual ground distance. To get the unit of measurement on the map, one has to measure the length of the line in centimetres.



Short-line scale

A long line-scale consists of a long line that is sub-divided into several equal parts. It has two sections: the primary section and the secondary section.



Linear scale

Properties of linear scales

  1. The scales are expressed graphically in the form of a line.

  2. They show the specific units of measurement.

  3. They give a direct measure of the distance on the ground represented by the corresponding distance on the map.

  4. The scale has the advantage of remaining the same even after the map is reduced or enlarged.


 

Classification of scales based on their sizes

Based on sizes, the scales are classified into three categories:

  1. Small scales

  2. Medium scales

  3. Large scales


Small scale

A map drawn using a small scale is called a small-scale map. A small-scale map has the following characteristics:

  1. It represents a large area of the earth’s surface on a piece of paper.

  2. The features on a small scale map appear crowded and closer to each other than they really are. As a result, they are not seen clearly.

  3. The map shows fewer details as it covers a large area on a piece of paper e.g. an atlas map of the world, Africa or Tanzania. It only gives a general picture of the area represented.


 

Examples of small scales are: 1:10,000,000 or 1 cm:100 km; 1:1,000,000 or 1 cm:10 km

Medium scale

This is a scale ranging between a small scale and a large scale.

Examples of medium scales are: 1:500,000 or 1 cm:5 km; 1:250,000 or 1 cm:2.5 km

Large scale

A map drawn using a large scale is called a large-scale map. A large-scale map has the following properties:

  1. The map shows many details of a small area on a piece of paper, e.g. a map drawn to represent a small area such as a town, a certain location or village etc. Therefore, more features can be represented on a large scale map.

  2. The map appears large in size though it represents a small part of the earth’s surface.

  3. The features on the map are large in size, so they can be seen quite clearly.


Examples of large scales are: 1:50,000 or 1cm:.0.5km; 1:25,000 or 1cm:.0.25km

Difference between Signs and Symbols

Distinguish and explain signs from symbols

 

The natural and artificial landscape features are represented on maps by means of symbols and signs. Symbols and signs are the alphabet or language of maps. As symbols and signs are

important in giving information on a map they should have the following qualities. They should be.

  1. Easy to read;

  2. Easy to understand;

  3. Easy to interpret; and

  4. Correctly and clearly shown and presented on any map.


Symbols and signs are commonly shown at the key or reference or legend of the map. With the aid of a key, reference or legend we can read and interpret a map. Symbols that are used in maps usually look like the natural and artificial features they represent. Signs usually do not look like the features they represent. Also most of the symbols are pictorial while most signs are not.

The symbols and signs used on maps are used to improve the appearance and readability of the map. Various symbols are used to depict features such as buildings, mines, forests, water bodies, farmlands, etc.









Symbols and signs often used in maps

 

 

 

 

 

Quantitative Information on Maps

 

The Distance on the Map and Converting to the Actual Ground by Using

 

Scale

 

Measure the distance on the map and convert to the actual ground by using scale

 

One of the many tasks that a map reader might encounter when reading maps is to take measurements. Measurements on maps involve:

  1. measurement of distances; and

  2. calculation of areas on maps.


The conversion of map distances and areas into actual ground distances and areas requires the application of scales. A distance is the length between two specified points on a map. V

Measurement of distances on maps

Distances on maps can either be straight or curved (bent). A straight or regular distance is one that has no bends or curves while a curved (or irregular) distance is the one with bends or curves.



Tools for measuring distances

There are three main tools that are used for measuring distances on maps. These are:

  1. a long, thin string or thread;

  2. a piece of paper; and

  3. a pair of dividers.


Measurement of distance using a thread or string

A long, thin string such as sewing thread can be used to measure a stretch of many curves or bends. This is the commonest method used by geography students to estimate distances on maps. This method is also used to estimate straight distances.

Procedures

  • Identify the distance to be measured on the map (e.g. a river, road, railway line, etc) and mark its two ends with a sharp pencil. Mark one end as A and the other as B.




Starting from one end of the string, trace the route (river, road, etc) with a string as shown in the figure below



  • Mark the string with an ink at point B.


 

  • Using a ruler or linear scale, measure the length of the string between point A and B and estimate the actual distance on the ground using the scale of the map provided.


 

Example 2

 

If the length of the section of the string between A and B is 20 cm and the scale of the map is one centimetre to one kilometre, then the length of the route on the ground is 20 km. Measurement of distances using a piece of paper

A piece of paper can also be used to measure straight and irregular (curved, bent) distances

Measuring straight distances

Procedures

  • Locate the distance to be measured on the map and mark its two ends as A and B using a sharp pencil.

  • Take a piece of paper, fold it to form a straight edge and lay the edge along the line AB and mark the exact length of the line on the edge of the paper as shown in the figure below.


 



 

  • Transfer the paper to a linear scale (or ruler) as indicated in the figure below so that the left hand mark (A) is on 0 (zero).




  • Use the provided scale to estimate the actual ground distance.

  • Identify the length to be measured on the map. Use a sharp pencil to mark both ends A and B.

  • Divide the route into sections which are more or less straight as shown in the figure below.




  • Lay the straight edge of the paper on the first straight section of the route. Mark with your pencil where the route bends (point 1).




  • Continue shifting the paper and marking the other distances between the points on the route.



  • Remove the marked paper, and using a ruler, measure from where you started to the last mark on the paper. If this distance is 20 cm and the scale is 1 cm to 1 km, then the distance of the route between A and B is 20 km.


Measuring distances using a pair of dividers

Measuring straight distances procedures

  1. Locate the distance to be measured on the map and mark its two ends using a pencil.

  2. Use a pair of dividers to measure the distance between the two end points on the map.

  3. If the distance is longer than the length of the dividers even when fully stretched measure the distance in sections and then sum up the lengths of all sections to get the total length.

  4. Place the divider on the linear scale and read the distance. Then use the scale to convert the obtained map distance into the actual ground distance.


Measuring irregular (curved or bent) distances

  1. Division method

  2. Stepping method Division method Procedures

  3. Divide the river, road, railway, etc into many, short straight distances.

  4. Open your dividers and measure all distances as shown in the figure below

  5. Add up the map lengths of all sections along the route.

  6. Use the linear scale to get the actual ground length from the sum obtained in (iii) above. The length of the route is equal to the sum of all sections, divisions or short distances.




Add up all the measurements: AB = 1 km; BC = 1 km; CD = 1 km; DE = 2 km; EF = 0.5 km; FG = 2 km; GH = 0.5 km; HI= 1 km; IJ = 2 km = Total length = 10 km.

Stepping method



    1. Circle = πr2 or πD2/4, where r = radius, D = diameter and π = 3.14 or 22/7

      1. Triangles = ?bh, where b = length of the base and h = length of the height.Open and set the pair of dividers to a known distance by using the linear scale e.g. quarter or half a kilometre as shown in the figure below.





    • Follow the river, road or line by stepping along it using the set dividers.


     

    • Add up the number of steps and multiply by quarter or half a kilometre (depending on the set length).


    Example 3

     

    Suppose number of steps when the divider is opened to a quarter kilometres wide is 20 and when it is a half, kilometre is 10. Then, the length of the route is:

     

    10 x ? = 5 or 20 x ? = 5 kilometres

     

    Note that if the distance of the last step is less than the set distance of the dividers, measure it separately and estimate its distance on the linear scale. Add up this distance to the total distance from the steps to get the full distance of the route (river, road or line).

     

    Areas of Regular and Irregular Figures

     

    Calculate areas of regular and irregular figures

     

    The figures whose areas are to be calculated on maps can either be regular or irregular

     

    Calculating areas of irregular shapes

     

    Features with regular shapes on maps are rectangular, triangular, square or circular. Finding the areas of such figures is simple. Mathematical formulae are used to calculate their areas. However, it is not common to find regular features on maps.

     

    Calculating areas of different regular shapes

     

    1. Triangles = L x W, where L = length and W = width.


     

    1. Squares =L2, where L = length of the side of a square.


     

    1. Triangles = ?bh, where b = length of the base and h = length of the height.


     

    1. Circle = πr2 or πD2/4, where r = radius, D = diameter and π = 3.14 or 22/7


     

    Calculating areas of irregular shapes: Features with irregular shapes are very common on maps. These may include shapes of lakes, forests, plantations, settlements, marshy land, etc.



    1. Calculate the areas of the rectangles, squares and triangles using mathematical formulae.An irregular shape 

      There are three methods used to calculate areas of irregular shapes. These are the:

       

      1. division method;


       

      1. tracing method; and


       

      1. grid square method.


       

      Division method

       



Thanks for reading!
Geography Geography Form One Topi 6
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