The Collaborative International Dictionary
Cartogram \Car"to*gram\, n. [F. cartogramme.] A map showing geographically, by shades or curves, statistics of various kinds; a statistical map.
n. 1 (context dated English) ''Generally'', a map used to indicate geographically-bound statistical information, typically region-by-region values of a given variable, for example by using different shadings for different ranges of values. 2 ''Specifically'', a map-like graph where the relative areas of graph regions are proportional not to the relative areas of the land regions they represent, but rather to another quantitative variable, such as population or gross domestic product.
A cartogram is a map in which some thematic mapping variable – such as travel time, population, or Gross National Product – is substituted for land area or distance. The geometry or space of the map is distorted in order to convey the information of this alternate variable. They are primarily used to display emphasis and for analysis as nomographs.
Two common types of cartograms: area and distance cartograms. Cartograms have a fairly long history, with examples from the mid-1800s.