NWP105A: Use maps, plans and drawings

Scales and distance

Scale bars

Maps need to be able to show how distance on the ground corresponds to distance on a map. This is often done using a scale bar.

scale bar showing 1:100,000 units

If a map is using a scale of 1: 100 000, one unit of measure on the map represents 100 000 units of measure on the ground. In this case, one centimetre on the map represents 100 000 centimetres, or one kilometre on the ground.

Maps can be described according to their scales. For example:

  • Large scale maps such as those used for house plans or road directories
  • Medium scale maps often used in topographic maps
  • Small scale maps like those used in atlases and world maps.


How can we calculate distance using a map?

Common scales

The scale that's used depends on what the map is being used for. For example, if you are travelling from one side of the country to the other you would use a small scale map, such as 1: 250 000. For every centimetre on the map, you would be travelling 2.5 kilometres (250 000 centimetres).

If you were travelling on foot, you would use a large scale map, such as 1: 50 000. For every centimetre you would be walking 500 metres (50 000 centimetres).

See how it works on the map below:

Please download the Adobe Flash Player from www.adobe.com to view this interaction, or use the text alternative instead.

Measuring distances

Once you know how a map scale works you can work out the distance between two points on a map using a ruler.

REMEMBER: You can't work out distance on a map unless it has a scale.

  • paper with points A and B marked, lying on a map
  • paper with points A and B next to a map scale
  • divider with points on A and B marked on a map
  • divider with one point placed against a ruler and the other 4.5cm on the ruler

1. Measuring distance between two points.

Set a straight edge of a piece of paper or card along the line on the map to be measured, and mark the paper carefully adjacent to the two end points A and B.

2. Lay the marked slip of paper along the scale line of the map, with the part marked A at zero.

Measure the length on a ruler to find the full distance between the two points A and B.

Ask your teacher or supervisor to give you more practice measuring distances with real maps. You can ask for tips on how to measure distances between two points when your have to travel around hills up and down valleys also.

3. Measuring distances using a divider

Open the divider and place the two points on the map, one on Point A and the other on point B

4. Place the open divider onto a ruler placing one point at 0 and measure the distance between the two divider points. Write your measurement down.