Understanding Map Scales

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 ScaleFraction
50 inches to 1 mile1:1,250
25 inches to 1 mile1:2,500
10 cm = 1 km1:10,000
6 inches to 1 mile1:10,560
2½ inches to 1 mile1:25,000
2 cm = 1 km1:50,000
1 inch to 1 mile1:63,360
1 cm = 1 km1:100,000
½ inch to 1 mile1:126,720
2 cm = 5 km1:250,000
¼ inch to 1 mile1:253,440
1 cm = 5 km1:500,000
1 inch to 10 miles1:633,600
1 cm = 10 km1:1,000,000

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.