Cartograms are maps in which symbol sizes represent some measured quantity. Maps that use area preserving projections can be considered cartograms; however, the term usually refers to a combination of statistical map and graph distorted to represent social phenomena. This involves a coordinate transformation Cartograms———19 to ensure that aspects of the original geography are preserved, while areas representing the chosen phenomenon and symbols do not overlap.
It is impossible to retain the locations, shapes, and adjacencies of the original map in a cartogram. Various techniques aim to minimize errors in these characteristics and aid recognition, while ensuring computational efficiency. Cartograms are used in spatial analysis, modeling, and geovisualization when studying social phenomena. Most are equal population cartograms, whereby the sizes of discrete areas relate to the numbers of inhabitants