Linear scale

Table of Contents

Read here about a type of scale. The relevance of this "scale" to the broader concern of "scale" as an "order of magnitude" is discussed.


Linear scale is the general term for the scale on a map. Also called a bar scale, scale bar, graphic scale, or graphical scale, it is a means of visually showing the scale of a map, nautical chart, engineering drawing, or architectural drawing.
In most projections such as Mercator, scale varies with latitude, so on small scale maps, covering large areas and a wide range of latitudes, the linear scale must show the scale for the range of latitudes covered by the map.

Mercator varying linear scale, from Defense Mapping Agency World Map, series 1150. Public Domain.

Nautical charts do not feature a linear scale since a nautical mile is approximately equal to a minute of latitude and can be measured against the latitude scale at the sides of the chart.
While linear scales are used on architectural and engineering drawings, particularly those that are drawn after the subject has been built, many such drawings do not have a linear scale and are marked "Do Not Scale Drawing" in recognition of the fact that paper size changes with environmental changes and only dimensions that are specifically shown on the drawing can be used reliably in precise manufacturing.


The linear scale is a type of proportional scale, one example of an operational definition of how one scale is mapped onto another scale, and how such information is communicated to people.