Idea 21of 22Builds onA map scale is a ratio
From kilometres back to the map
How long should a 30 km trip be on the map?
Today you'll discover
- why the map line is shorter
- how many scale bars fit
- when to multiply and when to divide
Think firstScale: 1 cm to 10 km. The trip is 30 km
How long should the ferry line be on the map?
Decide first, then press Next. Ask how many scale bars fit in the real distance.
A small map with Dock and Island joined by a dashed line marked 30 km for real, and a scale bar: 1 cm to 10 km. Then three copies of the bar, each marked 10 km, slide along the line; a ruler under it reads 3 cm; and the working says 30 km ÷ 10 km = 3, so 3 cm on the map. The last step shows a map at 1 cm to 4 km and a 20 km drive.
See the whole ideathe big idea and the key word, in one place
The big idea
To draw a real distance on a map, divide it by the kilometres per centimetre.
Compare themMap to real: 4 cm × 5 km = 20 km. Real to map: 30 km ÷ 10 km = 3 cm. The scale works both ways.
Easy to get wrongA map line is always much shorter than the real trip. If your map answer is bigger, you multiplied when you should have divided.
Key word
- scale drawing
- a drawing, like a map, where every length is the real length shrunk by the same ratio
Ready to use it?
- Find a map length from a real distance.
- Decide whether to multiply or divide by the scale.