Graphical scale and its importance

A graphical scale (bar scale) is a line drawn on the map and divided into units that represent real ground distances, e.g. a bar marked 0, 100, 200, 300 m. Plain, diagonal and vernier scales are graphical scales.

Importance on the map

1. Distances can be read directly without calculation; the user need not know the RF.
2. It is unaffected by shrinkage or enlargement. Paper expands or shrinks with weather, and a map may be photocopied, enlarged or reduced. A numerical scale (1:5000) would then be wrong, but the graphical scale changes together with the map, so it stays correct.
3. Clear even to non-technical users, who can compare the bar with the map features by eye or with a divider.
4. Easy to use with a divider or strip of paper for measuring curved lengths.
5. Gives an idea of the area size at a glance.
6. Accuracy. A diagonal or vernier graphical scale can read up to a very small unit.

For these reasons, a graphical scale is always shown on a map along with the numerical RF.