Cartograms: Broadly defined as a map using statistical symbols, a more specialist usage defines a cartogram as a type of map transformation based on a scale other than a true scale. For example, a voting map of Britain may show the size of counties in relation to the numbers of voters in each electoral unit, or an economic cartogram of the world may show countries drawn in proportion to their per capita GNP. This map shows the countries that mostly contribute to global warming.

http://images.wri.org/map_cartogram_global_warming_large.gif