Cartograms

A cartogram is a map on which the underlying geography has been distorted to convey the distribution of some thematic variable. If the distorted features are linear, such as the lines of a subway system modified to show travel times, then the cartogram is termed a linear, or distance, cartogram. Without a qualifier, cartogram typically refers to the value-by-area cartogram, in which polygonal features, such as state or country boundaries, are reduced or enlarged based on a variable such as population (see Figure 1). Such area cartograms take two major forms—contiguous and noncontiguous—and have been used primarily within the domains of political cartography and epidemiology.

The first use of the area cartogram technique is difficult to pinpoint, but early examples were produced in France and Germany ...