kartogram

A kartogram, more commonly referred to in English as a cartogram, is a map in which the size or shape of geographic units is distorted to reflect a quantitative variable rather than land area. In a kartogram, the area of each unit encodes the value of the chosen statistic, such as population, GDP, or election results, while the geographic boundaries may be preserved to varying degrees.

Cartograms come in several approaches. Contiguous cartograms resize regions while keeping adjacency, producing a connected mosaic with distorted geometry. Non-contiguous cartograms resize regions independently and may introduce gaps between units. Stylized variants include Dorling cartograms, which replace units with circles sized to the variable, and rectangular or block-based cartograms that emphasize grid-like shapes. The construction often involves algorithms such as diffusion-based methods, which balance area accuracy with shape recognizability.

Historically, attempts to represent data geographically date back to the mid-20th century, with formal cartogram development in the 1960s and later enhancements. In the early 2000s, computational methods, notably diffusion-based cartograms by Gastner and Newman, improved the ability to produce world-scale maps that represent population or other metrics. Today cartograms are widely used in political science, demography, economics, and journalism to highlight disparities and relationships not evident on standard maps.

Advantages include revealing relative weights of regions and communicating data intuitively. Drawbacks include distorted geography that can hinder recognition of places, potential misinterpretation, and varying degrees of accuracy depending on the method used. Cartograms are most effective when used alongside traditional maps and clear labeling to aid interpretation.