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The scale of a map shows the relationship between a distance on the map and the corresponding distance on the ground. All maps are reduced from actual size, and most printed maps are drawn to a single consistent scale.
Scale can be described in several different ways:
1. Graphically as a line somewhere on the map (usually in the margin), marked with distances, such as miles or kilometres.
2. Verbally, as a statement, such as ‘1 inch to 1 mile’ or ‘2 centimetres = 1 kilometre’. Inches tend to be used on older maps and centimetres on newer maps, though some still use inches.
3. As a ratio or representative fraction (RF) such as 1:50,000 or 1:250,000
The following are a selection of verbal statements and fractions for common map scales:
| Verbal Scale | Fraction |
|---|---|
| 50 inches to 1 mile | 1:1,250 |
| 25 inches to 1 mile | 1:2,500 |
| 10 cm = 1 km | 1:10,000 |
| 6 inches to 1 mile | 1:10,560 |
| 2½ inches to 1 mile | 1:25,000 |
| 2 cm = 1 km | 1:50,000 |
| 1 inch to 1 mile | 1:63,360 |
| 1 cm = 1 km | 1:100,000 |
| ½ inch to 1 mile | 1:126,720 |
| 2 cm = 5 km | 1:250,000 |
| ¼ inch to 1 mile | 1:253,440 |
| 1 cm = 5 km | 1:500,000 |
| 1 inch to 10 miles | 1:633,600 |
| 1 cm = 10 km | 1:1,000,000 |
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Maps are often referred to as large-scale or small-scale, the bigger the number after the colon in the RF the smaller the scale of the map. What constitutes a large-scale or small-scale map varies; the Library uses the following definitions:
- Large Scale: larger than 1:25,000
- Medium Scale: 1:25,000 – 1:250,000
- Small Scale: smaller than 1:250,000
Items at a scale larger than 1:100 are often treated as architectural drawings or engineering plans rather than maps.