LINE SCALE

Introduction

Almost all maps have scales. Scales play an important role in maintaining the dimensional accuracy of a map. This chapter outlines the different ways that scale can be expressed. It also explains how to use a scale to convert a measurement on a map and find out the distance it represents in the real world.

Why is scale necessary?

The Earth is an enormous sphere, which has an area of around 510 million square kilometres. That is more than 66 times the size of Australia. Since the Earth is so massive, and many geographical maps are of large areas, it would be impractical to always create a map which was true to size.

Cartographers (people who create maps) often make vast spatial information more easily accessible by reducing the dimensions of the area which they are representing on a map. These measurements are ideally reduced until they are able to fit onto a page. It is important, however, that the accuracy of these dimensions is not distorted during this process. To prevent that from happening, a scale is often used. A scale is a ratio used to show how a dimension on a map corresponds with the dimension it represents in the real world.

Different ways to express scale

Written

Scales can be expressed in a number of ways. They are often written in the form of 1 unit to 'n' unit(s). This means that 1 unit on the map represents 'n' units in the real world. An example of this would be 1 centimetre to 1000 centimetres. In other words, 1 centimetre on the map represents 1000 centimetres on the ground (in the real world).

It is very important that when writing a scale, people do not write 1 centimetre equals 100 metres, since this equation would be impossible.

Linear

Scales are frequently featured in map legends (tables explaining the meaning of symbols, signs colours and abbreviations used on a map). In these legends, the scale is often in the form of a linear scale (or line scale). A linear scale is a horizontal line which is divided into sections. It shows how measurements on a particular map correspond with measurements on the ground.

Fraction

A scale can also be written as a ratio or a representative fraction. If a scale is written as a ratio, it appears in the form 1:n. If the scale is shown as a representative fraction, it is 1/n. If we use the example of 1 centimetre to 1000 centimetres, then it the scale would be represented by 1:1000 (ratio) or 1/1000 (fraction).

Conversions

Sometimes geographers need to know how far somewhere/thing is from somewhere/thing else. Rather than go out into the field and measure this distance, which could be quite time consuming and may require specialist equipment, geographers can use a scaled map of the area. By simply using a ruler and referring to the provided scale, a person can measure the distance on a map and calculate what it converts to in the real world. If the distance between two points on a map is 6.5 centimetres and the scale of that map is 1 centimetre to 10 000 centimetres (also 1:10 000 or 1/10 000), then in the real world the measured distance would represent 65 000 centimetres (or 650 metres).

Example 1.
Calculate: the distance 6.5 centimetres represents on a map which has a scale of 1 centimetre to 10 000 centimetres.
6.5 x 10 000cm= 65 000 centimetres

Now, simplify: this answer so that it is in metres. (Remember, there are 100 centimetres in 1 metre).
65 000 100= 650 metres

It must be remembered that when making conversions, scales are not always in the same units. Sometimes, maps feature scales which are 1 centimetre to 1000 metres (also 1:1000 or 1/1000). In this case, 6.5 centimetres on the map would represent 6500 metres (or 6.5 kilometres) on the ground.

Example 2.
Calculate: the distance 6.5 centimetres represents on a map which has a scale of 1 centimetre to 1000 metres.
6.5 x 1000= 6500 metres

Now, simplify: this answer so that it is in kilometres. (Remember, there are 1000 metres in 1 kilometre).
6500 1000= 6.5 kilometres

Large scale and small scale

Some maps are called large scale maps. These maps show a smaller part of the Earth's surface, but reveal more detail. They are called large scale maps because the features on them appear relatively large. There are also small scale maps. Small scale maps show a larger area of the Earth, by reducing the features to make them appear smaller.