Cartogram
A map that distorts the size of geographic regions so that each region’s area is proportional to a data variable — population, GDP, or any other quantity. Geography meets data encoding.
// 01 — The chart
What it looks like
A contiguous cartogram where each region’s area is proportional to its population. Familiar shapes are warped, but spatial relationships are preserved.
// 02 — Definition
What is a cartogram?
A cartogram is a map in which the geographic size of each region is deliberately distorted to be proportional to a statistical variable. Instead of showing accurate land area, a cartogram resizes regions so that more “important” regions (by the chosen metric) appear larger, and less important ones shrink.
This solves a fundamental problem with choropleth maps: large but sparsely populated regions dominate the visual, while small but densely populated regions (like city-states or small northeastern U.S. states) are nearly invisible. A cartogram gives every data point visual weight proportional to its actual value.
The trade-off is recognizability. As regions distort, the familiar outline of a country or continent becomes harder to recognize. Different cartogram types handle this trade-off differently — contiguous cartograms try to preserve shape, while Dorling cartograms abandon shape entirely in favor of clarity.
Origin: The concept dates back to at least 1868 when Émile Levasseur used proportional squares on maps in French textbooks. The term “cartogram” was popularized in the early 20th century. Modern algorithmic cartograms were made practical by Dougenik, Chrisman & Niemeyer in 1985 and later by Gastner & Newman in 2004.
// 03 — Anatomy
Parts of a cartogram
// 04 — Usage
When to use it — and when not to
- Small regions hold disproportionately important data (e.g., city-states, small states)
- You want to correct the large-region bias of standard choropleth maps
- Your variable is a total or absolute count (population, GDP, votes) rather than a rate
- You need a striking, attention-grabbing visualization for editorial or presentation use
- Comparing absolute magnitudes across regions is the primary goal
- Your audience has enough geographic literacy to recognize distorted shapes
- Your audience is unfamiliar with the base geography — the distortion will confuse them
- Precise geographic locations matter (e.g., navigation, logistics)
- Your data is already a rate or density — a choropleth may be more appropriate
- You need exact value comparisons — area perception is imprecise
- The number of regions is very small (< 5) — a bar chart is simpler and clearer
- You need to overlay other spatial layers (roads, rivers, etc.) on the same map
// 05 — Reading guide
How to read a cartogram
Follow these steps whenever you encounter a cartogram in the wild.
Read the title and understand the encoding variable
What is the region size proportional to? Population, GDP, CO₂ emissions? Without knowing this, the distortion is meaningless.
Orient yourself geographically
Try to identify familiar regions by their relative position and labels. The overall shape of the continent or country should still be roughly recognizable in a well-made cartogram.
Compare region sizes visually
The core message is in the relative sizes. Which regions have grown compared to a normal map? Which have shrunk? The regions that changed the most are the most interesting data points.
Look for surprises
The power of a cartogram lies in the unexpected. If a geographically small country suddenly dominates the map (e.g., Singapore by GDP per capita), that’s the insight worth noting.
Check for a reference map or legend
Good cartograms include a small undistorted reference map so you can compare. If one isn’t provided, mentally compare the cartogram to a standard map you know.
// 06 — Pitfalls
Common mistakes
No reference map provided
Fix: Always include a small, undistorted inset map so readers can compare the cartogram to real geography. Without it, many viewers won’t understand the distortion.
Excessive distortion destroys recognizability
Fix: If regions are so distorted that no one can identify them, the map fails. Consider using a Dorling cartogram (circles) or Demers cartogram (squares) when contiguous distortion gets extreme.
Using a cartogram for rate data
Fix: Cartograms encode values through area. Using them for rates (like percentage) double-encodes area — once through the geometry and once through the variable. Use a choropleth for rates instead.
Missing labels on distorted regions
Fix: When shapes are warped beyond recognition, clear labels become essential. Label every region or at least the ones that changed most dramatically.
Not explaining the encoding
Fix: A cartogram is unfamiliar to many audiences. Always include a clear title and subtitle explaining that region size = the data variable, not actual land area.
// 07 — In the wild
Real-world examples
Worldmapper.org
An extensive collection of world cartograms showing everything from population to internet users. Each map resizes countries proportionally, dramatically revealing global inequalities.
U.S. election cartograms
Used by news outlets to show the electoral college or popular vote, making small but electorally significant states like New Hampshire visible alongside Texas and California.
The Guardian — Olympic medals
Cartograms resizing countries by medal count, revealing how tiny nations like Jamaica or New Zealand punch above their geographic weight in certain sports.
// 08 — Quick reference
Key facts
// 09 — Variations
Types of cartograms
Cartograms come in several variants that make different trade-offs between geographic fidelity and readability.
Contiguous cartogram
Warps region shapes while keeping them connected. Preserves topology but distorts familiar outlines.
Dorling cartogram
Replaces regions with non-overlapping circles sized by the variable. Sacrifices shape for clarity.
Demers cartogram
Like Dorling but uses squares instead of circles. Easier to label and pack tightly in grid layouts.
Non-contiguous cartogram
Scales regions in place without warping their shapes. Gaps appear between them, preserving recognizable outlines.
// 10 — FAQs
Frequently asked questions
What is a cartogram?+
A cartogram is a map in which the geographic size of each region is deliberately distorted to be proportional to a statistical variable. Instead of showing accurate land area, a cartogram resizes regions so that more "important" regions (by the chosen metric) appear larger, and less important ones shrink.
When should you use a cartogram?+
Use a cartogram when small regions hold disproportionately important data (e.g., city-states, small states). It also works well when you want to correct the large-region bias of standard choropleth maps, and when your variable is a total or absolute count (population, GDP, votes) rather than a rate.
When should you avoid a cartogram?+
Avoid a cartogram when your audience is unfamiliar with the base geography — the distortion will confuse them. It is also a poor fit when precise geographic locations matter (e.g., navigation, logistics), or when your data is already a rate or density — a choropleth may be more appropriate.
Is a cartogram suitable for dashboards?+
Yes — a cartogram can work well in dashboards as long as the panel is large enough for readers to perceive the encoded values, has a clear title, and includes the legend or axis labels needed to interpret it.
What category of chart is a cartogram?+
Cartogram belongs to the Geospatial family of charts. Charts in that family are designed to answer the same kind of question, so they often work as alternatives when one doesn't quite fit your data.
How do you read a cartogram?+
Start with the axis labels and legend, then look at the overall shape before zooming into individual marks. Compare prominent features against the rest of the data, and verify any conclusion against the underlying numbers when precision matters.