Map and plan scale

Real distance from a measurement on a map or plan at a 1:n scale, distance on the document from the ground, or the document’s scale from two distances. Enlargements (2:1) included.

The ratio n compares two lengths expressed in the same unit.

Scale 1:n

the ratio between drawing and reality: 1 cm of the document is n cm of the ground. The larger n, the more the map covers and the less it details.

Large and small scale

1:25,000 is a large scale (1/25,000 > 1/1,000,000) and shows more detail; a world map is small-scale.

Enlargement

n below 1, written the other way round: 2:1 means a drawing twice the size of the object. Used in precision mechanics and microscopy.

Usual scales

1:50 to 1:200 for building plans, 1:25,000 for hiking, 1:250,000 for driving, 1:1,000,000 and beyond for atlases.

The uncertainty comes from the measurements: at 1:25,000 one millimetre of reading is worth 25 m. At very small scales (countries, continents), the map projection distorts distances; the stated scale is exact only along certain lines. The map gives the horizontal distance; for the length of a route with relief, see the slope tool.

Areas follow the square of the scale: at 1:25,000 one square centimetre covers 250 m × 250 m = 6.25 hectares; at 1:50,000, 25 hectares, and each symbol summarises four times more ground. A 1:100 model weighs and costs by laws in n² and n³.

Without a title block (photocopy, old plan, screenshot), the scale is recovered from an element of known length: a 90 cm door, a football pitch, a street measured online. A resized photocopy or PDF loses the printed scale.