Look at the park map on the board. The two trees marked here are an easy walk apart in real life. About how far do you think they sit, five metres, twenty metres, a hundred metres? What clue on the map could help you decide?

A scale (like 1:100) tells you how many real metres one centimetre on the page stands for. Watch three worked plans, each at a different scale, then we'll try one together.

5 m × 3 m classroom at 1:100 (1 cm = 1 m)

The real classroom is 5 metres long and 3 metres wide. At 1:100, each metre becomes one centimetre, so the plan is 5 cm × 3 cm. Count along the bottom (5) and up the side (3); each centimetre stands for a metre.

40 m treasure route at 1:1000 (1 cm = 10 m)

The treasure is 40 metres away from the start. At 1:1000, each centimetre stands for ten metres, so the route is only 4 cm on the page. The right-hand number got bigger and the picture got smaller.

12 m × 8 m school yard at 1:200 (1 cm = 2 m)

The yard is 12 m by 8 m. At 1:200, each centimetre stands for two metres, so the plan is 6 cm × 4 cm. The bigger the right-hand number, the smaller the picture compared to the real thing.

Today we explore: build a 1:100 plan of our own classroom on the grid. We'll start at the south-west corner of the room and walk round, calling out where each corner sits in metres. The pupil at the board plots each corner in turn.