Cartogram Construction
Also known as: Value-by-Area Map, Area Cartogram, Density-Equalizing Map, Anamorphic Map
A cartogram is a map in which the area of each region is rescaled so that it is proportional to some variable — population, votes, GDP — rather than to its true geographic size. The aim is to correct the visual bias of ordinary maps, where large but sparsely populated regions dominate the eye while small, populous ones nearly vanish, by making each region as big as the quantity it represents. Cartogram construction is the family of techniques that produce these value-by-area maps, ranging from contiguous density-equalizing diffusion to non-contiguous circle and rectangle methods, each balancing the accuracy of areas against the recognizability of shapes.
Key highlights
- Removes the area-size bias of ordinary maps, sizing regions by the quantity that matters.
- Makes count-like variables such as population and votes directly comparable by area.
- The Gastner-Newman diffusion method preserves contiguity and topology while equalizing density.
- Non-contiguous and Dorling forms give crisp, easily compared shapes for clear value reading.
Intuition
This section is available to Pro members. Upgrade to Pro
How it works
This section is available to Pro members. Upgrade to Pro
When to use it
Use a cartogram when the geographic size of regions would mislead readers about a variable that is really about people or activity — most famously for election maps, where vast rural districts visually overwhelm dense urban ones on a conventional map. They suit population, votes, economic output, disease burden, and similar count-like variables where you want the eye to weigh regions by quantity rather than land area. Contiguous diffusion cartograms are best when keeping the map connected and roughly recognizable matters; Dorling and rectangular cartograms when easy value comparison outweighs geographic fidelity. They are poor choices when precise location, true distances, or unfamiliar regions are essential, or when the audience cannot invest effort in reading a deliberately distorted map; in those cases a normalized choropleth or proportional-symbol map is safer.
Strengths & limitations
- Removes the area-size bias of ordinary maps, sizing regions by the quantity that matters.
- Makes count-like variables such as population and votes directly comparable by area.
- The Gastner-Newman diffusion method preserves contiguity and topology while equalizing density.
- Non-contiguous and Dorling forms give crisp, easily compared shapes for clear value reading.
- Distorts familiar geography, so unfamiliar or oddly shaped regions can become unrecognizable.
- There is an unavoidable trade-off between area accuracy, shape fidelity, and topology.
- Requires positive values and careful handling of zeros, negatives, and very large outliers.
- Readers untrained on cartograms may misread the distorted map or distrust it.
Common pitfalls
This section is available to Pro members. Upgrade to Pro
Applications
This section is available to Pro members. Upgrade to Pro
Frequently asked
What is the difference between a contiguous and a non-contiguous cartogram?
A contiguous cartogram, such as the Gastner-Newman diffusion type, keeps every region connected to its true neighbours while deforming their shapes so that each area becomes proportional to its value; the map stays a continuous, if warped, sheet. A non-contiguous cartogram, including the Dorling circular form, instead resizes regions independently and lets them separate or be replaced by simple shapes, sacrificing connectivity and outline in exchange for accurate areas and clear, easily compared symbols.
How does the Gastner-Newman diffusion method work?
It treats the mapped variable as a density spread over the map and then lets that density flow according to the physics of diffusion — the same equation that describes how heat or a dissolved substance spreads to even out concentration. As the density equalizes, the region boundaries are carried along by the flow, so dense regions swell and sparse ones shrink until every region has the same density, which means its area is now proportional to its value. Because the boundaries move continuously, the regions stay connected and their topology is preserved.
When should I use a cartogram instead of a choropleth map?
Use a cartogram when the quantity you are mapping is a count or total — population, votes, cases, dollars — and you want regions to be visually weighted by that amount, correcting the bias that makes large empty areas dominate a normal map. Use a choropleth when you are mapping a rate, ratio, or density and want to keep true geography intact, shading each region by its value. The two are often most powerful together: a cartogram for magnitude and a choropleth for intensity.
Sources
- 1.Gastner, M. T., & Newman, M. E. J. (2004). Diffusion-based method for producing density-equalizing maps. Proceedings of the National Academy of Sciences, 101(20), 7499–7504.
You have read it. What now?
Cite this page
ScholarGate. (2026, June 22). Cartogram Construction. ScholarGate. https://scholargate.app/human-geography/cartogram-construction