I-GUIDE VCO: An Overview of Cartograms and Gastner’s Flow-based Algorithm

A cartogram is a data visualization technique consisting of a transformed map projection such that the area of each region is proportional to some given data value. Most modern algorithms produce cartograms that are contiguous, meaning that the topology of the original map is preserved. Cartograms date back to at least the year 1929, when The Washington Post published a cartogram illustrating “population and taxation”. Nowadays, cartograms are widely used in the social sciences and often appear in academic papers. In more recent years, cartograms have also seen a revival in a variety of news publications, marking their relevance beyond the academic domain. Cartograms that illustrate the number of votes for election districts are a notable example of this. The Gastner-Newman Algorithm, which relies on the diffusion equation, is currently the most popular method for producing contiguous cartograms. However, Gastner et al. recently developed a method that relies on different flow-based equations to realize further speed increases in the cartogram generation process.