cartogram

A cartogram is a map in which geographic space is intentionally distorted so that the size of each area is proportional to a specified variable, such as population or economic output. Unlike conventional maps, the geometry, area, or even adjacency of places can be altered to emphasize the distribution of the chosen statistic, making spatial patterns more immediately apparent.

There are several approaches. In contiguous cartograms, the borders are deformed so that regions remain connected, preserving some sense of location and adjacency. Non-contiguous cartograms resize units independently, often creating gaps between regions. Dorling cartograms replace areas with circles scaled to the data and placed at approximate locations. Rectangular cartograms approximate regions as rectangles arranged to fit a grid. Density-equalizing cartograms, a widely used class, apply a diffusion-based algorithm to resize areas so that their total map area matches the variable while preserving topological relationships.

Uses and examples include visualization of population distribution, GDP, literacy, language prevalence, disease incidence, or election results. The Worldmapper project and various statistical agencies publish cartograms to illustrate global or regional data, and they are commonly employed in journalism and education to highlight imbalances that are less evident on standard maps.

Limitations and interpretation considerations include distortion that can hinder recognition, mislead about distance or shape, and challenges in extracting exact values. Cartograms trade geographic fidelity for data emphasis, requiring careful legends and context. Producing readable cartograms often involves specialized algorithms and software.