In How Far? The Scale Bar you used a scale bar. Big maps also give their scale as a ratio, which works like the scale drawings of math class.
Key idea
A scale such as 1:100,000 means 1 unit on the map stands for 100,000 of the same unit on the ground: 1 cm on the map is 100,000 cm, or 1 km, in real life.
Why it works
A ratio has no units, so it works in any unit: 1 inch on a 1:100,000 map is 100,000 inches on the ground too. The only work is changing a large number of centimeters (or inches) into kilometers (or miles). Remember: 100 cm = 1 m and 1,000 m = 1 km, so 100,000 cm = 1 km.
Worked example: Map to ground
On a 1:50,000 hiking map, a trail is 6 cm long. How long is the real trail?
- Each cm on the map is 50,000 cm on the ground.
- 6 × 50,000 = 300,000 cm.
- 300,000 cm ÷ 100 = 3,000 m = 3 km.
Answer: 3 km.
Worked example: Ground to map
Two towns are 40 km apart. How far apart are they on a 1:1,000,000 map?
- On this map 1 cm stands for 1,000,000 cm = 10 km.
- 40 km ÷ 10 km per cm = 4 cm.
Answer: 4 cm.
| Scale | 1 cm on the map is | Kind |
|---|---|---|
| 1:10,000 | 100 m | Large scale: a neighborhood, lots of detail |
| 1:100,000 | 1 km | Medium: a county |
| 1:10,000,000 | 100 km | Small scale: a continent, little detail |
Common mistake
Thinking a "large-scale" map shows a large area. It is the other way around. Scale is a fraction: 1/10,000 is a larger fraction than 1/10,000,000, so a 1:10,000 map is large scale, shows things larger, and covers a small area in great detail. A world map is small scale.