Taxonomy of Data Visualization Methods - Data Visualization: A Successful Design Process - page 150

Dorling cartogram
Data variables : 2 x categorical, 1 x quantitative-ratio.
Visual variables : Position, size, color-hue.
Description : A Dorling cartogram (named after Professor Danny Dorling who
invented them) deploys a uniform shape (typically a circle) to represent a geographical
location and then sizes this according to a quantitative variable. In the following
example, we see a portrayal of countries represented by circles, sized according to that
country's CO2 emissions and colored to distinguish the continents. As before, we may
struggle to easily identify places that have now been transformed in shape, size, and
position but effective annotation can generally compensate for that.
Image from "An atlas of pollution: the world in carbon dioxide emissions" ( http://image.guardian.
co.uk/sys-files/Guardian/documents/2011/02/10/CarbonWeb.pdf ), created by Michael Robinson,
Mark McCormick and Paul Scruton