According to Wikipedia:
A cartogram is a map in which some thematic mapping variable – such as travel time, population, or GNP – is substituted for land area or distance. The geometry or space of the map is distorted, sometimes extremely, in order to convey the information of this alternate variable.
This cartogram of the United States rescales the size of each state in proportion to the number of representatives of its congressional delegation, which is apportioned based on the state's population. Space is discretized by a hexagonal grid to afford states a minimum width and length. For each of its members of Congress, a state is allotted 13 hexagons.
Read this blog post to learn how this cartogram was created.