Geography: Grade 7
Map Skills: Distance & Scale
DISTANCE AND SCALE
The ability to use and interpret maps is an important part of geographical skills.
A map shows what an area looks like when drawn on a flat piece of paper. It always
appears much smaller than the actual area it represents. Maps also show the features on
the Earth’s surface.
Physical Map of the World
Wikimedia Public Domain
When using a map, remember:
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It has been drawn to a scale;
The features and landforms are seen as if shown from above, looking down on the
landscape;
Symbols are used to show characteristics and features.
Different kinds of maps are drawn for different
functions.
A cartographer is someone who compiles maps.
In the past, maps were drawn by hand, but today they
are drawn using modern computer technology.
Hand Drawn World Map, 1689
Wikimedia Public Domain
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Geography: Grade 7
Map Skills: Distance & Scale
Map Scale
We have seen that a map is a reduction of reality, as seen from above. To reduce a map in
this way, you have to use a certain scale. The scale of a map should always be shown at
the bottom of the map, as this enables you to calculate the distance between two places.
Different kinds of scales can be used on a map.
Word Scale
On some maps, you will see that words and figures are used to describe the scale, for
example, 1 cm represents 20 km. This means that 1 cm on the map represents 20 km in
reality.
If the distance between two places on the map is 3 cm, you can then calculate the distance
between the 2 points, i.e. 3 cm x 20 = 60 km.
Line Scale
On this scale, you can measure the distance between two places directly, using a ruler. A
line scale is shown on the map as a line on which divisions representing actual distance
are marked. You would then put your ruler against the scale to work out the distance.
Ratio Scale
This is shown on the map as a figure, which states the relationship between the distance
on the map and the real distance, expressed as a ratio (or sometimes a fraction).
If a map could be drawn to the same scale as real life, it would have a ratio scale of 1:1, if
it was 100 times smaller, for example, the ratio would be 1: 100.
A ratio scale of 1:100 000 means that the area on land is 100 000 times bigger than on the
map. So in this example, 1 cm on the map would equal 100 000 cm (1 km) on the map.
To measure distance on a ratio scale, if for example, two places are 2 centimetres apart on
a 1: 50 000 map, you would calculate as follows:
2 x 50 000 = 100 000 cm = 1 km
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Geography: Grade 7
Map Skills: Distance & Scale
On a map with a scale of 1: 25 000, the grid lines are 1 cm apart, so a quick way to
estimate distance from one place to another, is to count the number of squares between
the places. The distance diagonally across a square on a 1: 25 000 map is 1,5 km.
Large and Small Scale Maps
We saw in Grade 6 that a detailed map is known as a large scale map, as it shows objects
as large, as well as a lot of information about a small area. A street map is an example of a
large scale map. Large scale maps show a large amount of details, although the ratio in
the scale is small.
The Google map below is a large scale map and has a line scale, where 2 cm is equal to
500 m. We need to convert this to kilometres and calculate as follows:
2:500, therefore 1:250, i.e., 1 cm on the map represents 250 metres on the ground
(0,25 km).
There is 100 cm per metre.
250 x 100 = 25,000
On a ratio scale, this would be written as 1:25 000.
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Large Scale Map
A ratio scale of 1:5000 is usually used for a town plan and would show details such as
streets and schools. It would show more detail than the map above.
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Geography: Grade 7
Map Skills: Distance & Scale
A small scale map does not show a lot of detail and any objects shown are very small. An
example of a small scale map would be a world map.
The Google map below is a small scale map and has a line scale, where 1 cm is equal to
2 000 km. On a ratio scale, this would be written as 1: 200 000 000. There are 100 000 cm
in 1 km (2000 x 100,000).
Small Scale Map
So the smaller the number on the map scale, the more detailed the map will be.
A 1:100 000 map will show map 10 times larger than a 1: 1 000 000 map, but will only
show a tenth of the land area on the same size of paper.
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Geography: Grade 7
Map Skills: Distance & Scale
Measuring Distance
By measuring distance on a map, you can work out how far the distance is in reality.
There are two ways of doing this:
1. Measuring the direct distance between two points, by using a straight-line
measurement (as the crow flies), with a ruler.
Once you have your measurement between the two places, you then use the scale to
calculate the distance.
For example, if your measurement is 10 cm and the line or word scale shows that 100 km
is equal to 1 cm, then the distance would be 1000 km.
If using a ratio scale of say, 1:10 000 and you measure 5 cm between the 2 points, then
the distance would be 50 000 cm, which is 50 km.
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Geography: Grade 7
Map Skills: Distance & Scale
2. Measuring the indirect distance between 2 points. This is following the actual route
that you would use when travelling by car along the roads, for example.
To follow the actual route, you can use a piece of string and stretch and bend it between
the 2 points to be measured, following the exact shape of the road. You then mark off the
distance on the string.
If using a line scale, you can place the string on the line scale of the map to work out the
distance. If using a word scale, you would measure the piece of string with a ruler.
Example
If the string measures 15 cm from Point A to Point B and the word scale shows that
1 cm = 5 km, you can calculate that the distance is 15 cm x 5 = 75 km.
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