Scale

How can a huge place fit on a small piece of paper? Thanks to the map's scale.

Go back to the map of a small city. Each centimetre on the map stands for a certain distance on the ground. Suppose it is 500 metres; then we say the scale is 1 cm = 500 m. The map is not smaller by accident: it is shrunk by a known, fixed amount, and the scale tells you exactly how much.

Here is the idea with your own journey. If your school is 10 km from home, you cannot draw a 10 km line in your notebook. You draw a 2 cm line instead, and write the scale 1 cm = 5 km beside it.

Now a bigger map. On the book's map of India, the scale is a small ruler in the bottom left corner, with '500' above it and 'km' at the side. It means that this ruler, which is 2.5 cm long on the printed map, stands for 500 kilometres on the ground.

Notice that the two maps shrink by very different amounts. On the city map one centimetre is half a kilometre; on the map of India one centimetre is 200 kilometres. Same size of paper, very different scales.

So the real distance between two points on a map depends on the scale the map is using. If someone tells you two places are 3 cm apart on a map, you still know nothing about how far apart they really are, until you are told the scale.

The book sets a neat exercise: draw a school playground, 40 m by 30 m, at a scale of 1 cm = 10 m. Your rectangle will be 4 cm by 3 cm. Then measure its diagonal in centimetres and use the scale to turn that back into metres.