GEOGRAPHY O LEVEL(FORM ONE) NOTES – MAP WORK

MAP WORK

A map is a scale representing the earth’s surface on a flat material, for example, a piece of paper, wall, clothes, or a piece of wood.

Map interpretation is the ability to translate the symbols and signs on the map into ordinary language by identifying the features they represent.

COMPONENTS / QUALITIES / ESSENTIALS OF A GOOD MAP

A map is good if it contains all the essentials of maps; therefore, the essentials are good qualities of maps.

The essentials of a good map are:

1. Key. Used to interpret symbols and signs found on a map. For example:

2. Title. Used to show what the map is all about. This is the heading of the map. It can appear on top of the map or anywhere else.
3. North direction. This indicates the north direction. It shows where north is, and by knowing north, one can know the direction and bearing of the place.

N

4. Margin. This is a boundary or limit around the map. It shows the reader and interpreter the end of the map.
5. Publisher and date of publication. This shows when the map was produced and the publisher.
6. Scale. It shows the relationship between map distance and the actual ground distance. For example, 1 cm to 10 km means one centimeter on the map represents ten kilometers on the ground.
7. Latitude and Longitude / Grid reference. Used to locate the place on the map. For example, the map of Tanzania is located at latitude 6°00′ south of the equator and longitude 35°00′ east of the Greenwich meridian.

TYPES OF MAPS

The classification of maps is based on the purpose for which each map is drawn. Therefore, maps can be categorized into three types as follows:

1. Sketch map
2. Atlas map / wall maps
3. Topographical maps

i) Sketch maps

A map drawn from observation (rather than from exact measurements) and representing the main features of an area.

ii) Atlas map / wall maps

A collection of different maps that have been bound together in one volume to form a book. These maps are usually drawn to scales and show towns and cities, hills, mountains, valleys, forests, countries, etc.

iii) Topographical maps

Show selected physical and human features in an area and their positions on the ground, for example, hills, villages, mountains, lakes, ponds, rivers.

MAP SCALE

Is the relationship or ratio between map distance and actual ground distance.

Scale = map distance / Ground (actual) distance.

TYPES OF SCALE

We can classify the scale according to the size in our criteria. There are three types of scales:

a) Large scale

Used to present information on small areas, for example, a map of village buildings and farms. The map size involves all numbers less than 1:25,000, e.g., 1:10,000 and 1:5,000.

Characteristics of large scale:

• It has smaller numbers in the denominator.
• It shows features clearly.
• It contains geographical details.

b) Medium scale

Used to represent medium details shown on the map. Map size involves numbers between 1:25,000 to 1:250,000, e.g., 1:50,000 and 1:100,000. Examples include maps of districts, regions, cities, etc.

c) Small scale

Used to present information that covers a large area with less detail. For example, a map of a country, continent, or world. May involve numbers between 1:500,000 to 1:1,000,000.

Characteristics of small scale:

• It has the largest denominator.
• Contains a lot of geographical information.
• It does not show geographical features clearly.

WAYS USED TO EXPRESS MAP SCALE

1. As a statement. Refers to the scale expressed in words or explanation. For example, one centimeter on a map is equivalent to 10 kilometers on the ground.
2. Linear scale. Also called plain or graphic scale. This is a line divided into two parts: the primary division and secondary division. The secondary divisions are expressed in meters and placed on the left side from zero, and the primary divisions are expressed in kilometers and placed on the right side from zero.

3. Representative fraction (RF) scale. Written as a ratio, e.g., 1:50,000. The distance on a map is expressed as a fraction of the actual distance on the ground.

RF scale = map distance / Ground distance

– The top number (numerator) represents the map distance on the ground and is usually 1.

IMPORTANCE OF SCALE ON THE MAP

• Scale helps to calculate the area of a map.
• It enables us to calculate distance on a map.
• Scale shows the relationship between map distance and the actual ground distance.
• Scale helps us to enlarge and reduce the area on a map or the whole map.
• Scale can be used to calculate the vertical exaggeration on a map.
• Scale is used to calculate the gradient on a map.

Distinguish and explain signs from symbols

2) QUANTITATIVE INFORMATION ON MAPS

A) MEASURING DISTANCE ON THE MAP

Distance is the length of elongated features on the earth’s surface such as roads, railways, rivers, etc.

How to measure distance

To obtain the distance of any feature on the map, consider whether the distance to be measured is straight or curved.

Straight distance

For all straight distances, a ruler is used to obtain the distance directly from the topographical map given.

Curved distance

It becomes difficult to obtain curved distances of features by using a ruler directly from the topographical map when the area is inclined. In this case, the following devices can be used:

• I. A pair of dividers. A pair of dividers is commonly used to measure the distance. Start by breaking the length using the dividers, then transfer the measured straight lines to the linear scale or ruler for calculation to get the actual distance.
• II. A piece of string. Slowly measure the distance by a piece of string along the given length, then transfer it to a linear scale or ruler for actual calculation of the distance.

20 cm map distance

Scale distance = map distance / Actual distance

½ km = ½ × 2 = 1 km

1:50,000

1/50,000 = 20 cm

100,000 = 20 cm

50,000 × x = 10 km

1. A piece of strip paper

Slowly lay a piece of paper along a given length, then break your lengths into short segments and transfer to the linear scale for measuring and calculation.

MEASURING AREAS ON A MAP / CALCULATE AREA OF REGULAR AND IRREGULAR SHAPES

Area size refers to the bigness or smallness of an area on the earth’s surface, i.e., the bigness or smallness of the earth’s surface from a topographical map. Consider whether the area is regular or irregular.

Exercise

1. State the following:
   • a) A map is a scale representing the earth’s surface on a flat material.
   • b) Map reading refers to scale reading obtained from recognizing or identifying signs and symbols used on a map.
   • c) Scale is the relationship or ratio between map distance and actual ground distance.
   • d) Contour is a line drawn on a map which shows areas at the same height.
2. Why do we study maps?
   • i) People use them to reach their destinations.
   • ii) Builders use maps to build new roads.
   • iii) Maps are used in conducting various geographical researches.
   • iv) Maps are useful in military activities.
   • v) Maps are useful in describing the features on the earth’s surface.
3. State the ways of expressing scale:
   • i) Statement scale: expressed in words, e.g., 1 cm on the map is equivalent to 10 km on the ground.
   • ii) Linear scale: called plain scale, with primary and secondary divisions.
4. What is the importance of a scale?
   • – It helps to calculate the area of a map.
   • – It enables us to calculate distance on a map.
   • – Scale helps us to enlarge and reduce the area on a map.
5. List at least 3 methods of calculating the linear distance of an object:
   • i) A pair of dividers
   • ii) A piece of paper
   • iii) A piece of string
6. The distance of the road is 36 cm from Lindi to Nachingwea. Convert the distance in kilometers if the scale used is 1:100,000.

Solution:

Distance = 36 cm

Scale = 1:100,000

1 km = 100,000 cm

Hence, 1 cm = 1 km (after cross multiplication)

Therefore, 36 cm = x km

1 × x = 36 km

x = 36 km

Therefore, the distance on the ground from Lindi to Nachingwea is 36 km.

b) From the above, convert the same distance in km if the scale is changed to 1:50,000.

Solution:

Distance = 36 cm

Scale = 1:50,000

1 km = 100,000 cm

x = 50,000 cm (cross multiplication)

= 0.5 km

Therefore, the distance in kilometers is 0.5 km.

REGULAR SHAPE

These are areas with definite shapes such as squares, triangles, etc. Their total perimeters or areas are obtained by mathematical formulas, e.g., length × width, side × side.

IRREGULAR SHAPE

These are areas with indefinite shapes such as lakes, farms, ponds, etc. Their areas can be obtained by any of the following three methods:

• a) Square method
• b) Strip method
• c) Geometrical method

SQUARE METHOD

This is the most accurate and widely used method.

Square methods are normally used as follows:

• a) Count all full squares that are complete.
• b) Count incomplete squares and divide them by 2.
• c) Add them with the full squares to obtain the total area in km².

METHODS USED TO SHOW OR LOCATE POSITIONS OF A PLACE ON A MAP

The following are major methods used to show positions of a place on a map:

1. Grid reference
2. Place name
3. Bearing and compass direction
4. Latitude and longitude

Place name

You can locate the position of a place by where the features are found, e.g., Mbeya, Dodoma, Mtwara.

Grid reference

Grid reference is a network of vertical and horizontal lines on a map. Vertical lines whose numbers increase towards the east are called Eastings. Horizontal lines whose numbers increase towards the north are called Northings. Where horizontal and vertical lines meet or cross each other, they form a square known as a grid square (G.S). A grid reference point is written in the form of six digits starting with three digits of Eastings then three digits of Northings.

To write down the grid reference of points A, B, C, D:

• A = 12006
• B = 130065
• C = 140067
• D = 14003

LOCATION AND POSITION

COMPASS BEARING AND DIRECTION

Compass direction is divided into:

• a) 4 cardinal points
• b) 8 cardinal points
• c) 16 cardinal points

4 cardinal points

8 cardinal points

16 cardinal points

HOW TO FIND DIRECTION OF A PLACE ON A MAP

1. Identify the points on the given map. Points may be given by using grid reference points, place name, or letter.
2. Draw a straight line connecting the two points.
3. Mark the major four cardinal points at the starting point with the word “from”.
4. Look at the question asked then provide your answer.

Example: What is the direction of point A from B? The direction of point A is NW.

COMPASS BEARING

Bearing is a direction measured in degrees clockwise from north. They are written in three figures, e.g., 090°, 045°.

HOW TO FIND BEARING ON THE MAP

1. Identify the grid reference points given on the map.
2. Draw a straight line connecting the two points.
3. Draw the major four cardinal lines at the starting point.
4. Look at the question asked and use a protractor to measure degrees clockwise from north up to the line joining the two points.
5. Provide your answer in degrees, e.g., What is the bearing of point A from B?

BEARING

• a) Forward bearing
• b) Backward bearing

a) FORWARD BEARING

Is a bearing into a subject.

Procedures to calculate forward bearing:

1. Identify the two points.
2. Join them with a straight line.
3. Draw north direction on the second point.
4. Measure the angle by using a protractor.
5. State the bearing in terms of degrees of the direction.

Example: Find the forward bearing of Moa from Midland.

B = 135° SE

Find the bearing of Mbezi to Ubungo.

The bearing of Mbezi to Ubungo is 135° SE.

b) Backward bearing

Is the opposite of forward bearing; it’s taken from the object to the observer while forward bearing is taken from observer to the object.

How to determine the back bearing:

1. Find forward bearing.
2. Mark the cardinal point north direction of the opposite point.
3. Find the bearing of the observer along the straight line. The formula to determine the back bearing is:
   Back Bearing (BB) = Forward Bearing (FB) ± 180°
   If FB < 180°, then BB = FB + 180°
   If FB > 180°, then BB = FB – 180°

EXERCISE

Scale conversion

a) To change statement to RF scale: 1 cm represents 60 km

Solution:

1 km = 100,000 cm

60 km = x

RF scale = 1:6,000,000

b) One centimeter represents 0.75 km

Solution:

1 km = 100,000 cm

100,000 × 0.75 = 75,000

RF scale = 1:75,000

c) One centimeter represents two kilometers

Solution:

1 km = 100,000 cm

100,000 × 2 = 200,000

RF scale = 1:200,000

IMPORTANCE OF THE USE OF MAPS

• a) People use them to reach their destinations.
• b) Maps are used to describe the features of the earth.
• c) Builders use maps to plan the best use of the land.
• d) Road constructors use maps to construct new roads.
• e) Maps are useful in military activities.
• f) Maps are used in conducting various geographical researches.