Draw a square grid in the background. The lengths of the sides of the squares correspond to some distance, usually one kilometre. Make sure that you write down what this distance is, somewhere on the map. For the example, the squares would be 2cm across. Draw a scale bar on the map. This is a little bar, usually 1 or 2 cm across, labelled with how long it would be in real life. For the example, a scale bar 1cm long would be labelled 1/2 km. Write the scale (1:50,000) somewhere on the map. Some maps use a combination of these methods (e. g. the OS maps of Britain use all three).
The picture shows the process of plotting contour lines.
