What is scale?
A map is a much smaller drawing of the real world. Scale tells us how many times the ground has been shrunk to fit on paper. It is the fixed ratio between a distance measured on the map and the matching distance on the ground.
Scale can be shown in three ways:
- Statement scale — written in words, e.g. "1 cm represents 1 km".
- Representative Fraction (RF) — a ratio such as 1:50 000, meaning 1 unit on the map equals 50 000 of the same units on the ground.
- Linear (bar) scale — a marked ruler printed on the map that you compare distances against directly.
Key idea
Ground distance = map distance × scale. For 1:50 000, every 1 cm on the map is 50 000 cm (0.5 km) on the ground.
Measuring distance
To find a straight-line distance, place a ruler between the two points, read the map length, then multiply by the scale. To measure a winding distance such as a road or river, lay a piece of string or thread along every bend, mark the total length, straighten it against a ruler, then convert using the scale.
Example
On a 1:50 000 map two towns are 6 cm apart in a straight line. Ground distance = 6 × 50 000 = 300 000 cm = 3 km.
Large scale and small scale
A large-scale map (e.g. 1:10 000) covers a small area but shows great detail. A small-scale map (e.g. 1:1 000 000) covers a large area but shows little detail. Choosing the right scale depends on what you need to see.
Remember
- 1 km = 100 000 cm; 1 m = 100 cm.
- The smaller the RF number (1:10 000), the larger the scale and detail.
- Use string for curved routes, a ruler for straight ones.