Cartograms

Cartograms are maps in which the geometry or space of geographic areas is distorted to convey a quantitative attribute. Instead of representing land area or distance, cartograms resize regions so that their size, shape, or position reflects the magnitude of a variable such as population, gross domestic product, or election results. The resulting visualization emphasizes the spatial distribution of the variable and can reveal patterns that are less evident on traditional maps.

There are several approaches to creating cartograms. Area or contiguous cartograms preserve adjacency and the overall topology of regions, but their areas are proportional to the data values. These are often produced with diffusion-based methods that resize each region while maintaining borders. Non-contiguous cartograms shrink or expand each region independently, reducing overlap but breaking borders between neighboring regions. Dorling cartograms replace each region with a circle sized by the data value, while rectangular cartograms approximate regions by rectangles to simplify layout. Hybrid and other methods also exist.

Construction and challenges: Cartograms require choosing what to preserve—area, topology, or recognizability—and balancing accuracy with readability. They can be produced by algorithmic methods or manual adjustment. Common data types include population, wealth, energy use, or electoral influence. They are widely used in journalism, education, and research to illustrate disparities and relationships.

Limitations: Distortion can hinder recognition, and precise values are often not recoverable from the visualization. Labels may collide, and interpretation can be affected by the chosen distortion method. Effective cartograms use clear legends, consistent color schemes, and contextual information to aid understanding.

History: Modern density-equalizing cartograms gained prominence in the early 2000s, notably through diffusion-based algorithms. Since then, various techniques and software have broadened their availability and applications.