Dorling Cartogram
A map where geographic regions are replaced by non-overlapping circles whose sizes encode a data variable — making it easy to compare quantities while preserving approximate spatial positions.
// 01 — The chart
What it looks like
A Dorling cartogram of U.S. states where each circle’s area is proportional to population. California, Texas, Florida, and New York stand out as the largest circles.
// 02 — Definition
What is a Dorling cartogram?
A Dorling cartogram is a type of cartogram that replaces geographic regions (countries, states, districts) with non-overlapping circles. Each circle’s area is proportional to a data variable — such as population, GDP, or election votes — rather than the region’s land area.
Unlike traditional cartograms that distort the actual boundaries of regions, a Dorling cartogram abandons geographic shapes entirely. Instead, circles are positioned to approximate the original geographic layout. This makes comparison much easier because circles are simple shapes that our eyes can gauge accurately.
The trade-off is clear: you lose the precise outline of each region, but you gain an honest, comparable representation of the data. Large countries with small populations (like Canada or Russia) shrink, while small but densely populated areas (like the Netherlands or New Jersey) expand to their rightful visual prominence.
Origin: The Dorling cartogram was invented by geographer Daniel Dorling in 1996. His approach used circles positioned through a force-directed algorithm to prevent overlap while maintaining approximate geographic relationships.
// 03 — Anatomy
Parts of a Dorling cartogram
// 04 — Usage
When to use it — and when not to
- You want to compare quantities across regions without geographic size bias
- Population, GDP, or vote counts need honest visual weight on a map
- Your audience is familiar with the general geography so circles still make sense
- You need a cleaner, less distorted alternative to contiguous cartograms
- You have fewer than ~50 regions to keep the layout readable
- You want to add color encoding as a second data dimension on each circle
- Precise geographic boundaries or shapes are critical to the analysis
- Your audience is unfamiliar with the underlying geography
- You have very many regions (hundreds) — the layout becomes a packed mess
- You need to show spatial patterns like clustering or contiguity
- A simple choropleth map would communicate the message just as well
- The data variable has very little variation — all circles will look the same size
// 05 — Reading guide
How to read a Dorling cartogram
Follow these steps whenever you encounter a Dorling cartogram in the wild.
Read the title and legend first
Understand what data variable drives the circle sizes. Is it population, GDP, votes, emissions? Knowing the variable is essential before interpreting any circle.
Orient yourself geographically
Even though shapes are gone, circles are positioned approximately where the real regions sit. Look for familiar spatial anchors — coastal states, central clusters, or country groupings.
Compare circle sizes
The area of each circle is proportional to the data value. Larger circles mean higher values. Be careful: area grows with the square of the radius, so a circle that looks “twice as wide” is actually four times the value.
Look for color encoding
Many Dorling cartograms add a second variable via color. For example, circles sized by population might be colored by political party, income level, or growth rate. Check the color legend.
Identify outliers and clusters
Which circles dominate? Which are tiny? Are there clusters of similar-sized circles in one region? These patterns reveal the geographic distribution of the data.
// 06 — Pitfalls
Common mistakes
× Scaling by radius instead of area
The most critical mistake. If you double the radius for double the data value, the circle’s area quadruples — massively exaggerating differences. Always scale by area (radius ∝ √value).
× Losing geographic context
If circles drift too far from their real positions during layout, readers can’t identify regions. Always label circles and constrain displacement.
× Too many regions
With hundreds of tiny circles, the map becomes an unreadable packed bubble chart. Aggregate small regions or use a different chart type for large datasets.
× No legend for circle sizes
Without reference circles showing what size equals what value, readers cannot decode absolute magnitudes — only relative comparisons.
× Ignoring overlap artifacts
If your layout algorithm doesn’t fully resolve overlaps, circles can hide behind each other, misrepresenting the data.
// 07 — In the wild
Real-world examples
Election coverage
News outlets use Dorling cartograms to show electoral college votes by state, giving small but elector-rich states like Connecticut proper visual weight.
World population maps
Global Dorling cartograms sized by population reveal how India and China dominate while geographically vast countries like Canada and Australia shrink to small circles.
Public health dashboards
COVID-19 case counts by country or U.S. state were frequently shown as Dorling cartograms, ensuring New York and New Jersey weren’t hidden by their small land areas.
// 08 — Quick reference
Key facts
// 09 — Variations
Types of Dorling cartograms
The Dorling approach has inspired several related variations, each with unique trade-offs.
Standard Dorling
Non-overlapping circles positioned using a force-directed algorithm to preserve approximate geographic layout.
Demers cartogram
Uses non-overlapping squares instead of circles. Squares pack more efficiently and can carry labels more easily.
Graduated symbol map
Places proportional symbols at exact geographic centroids without preventing overlap, preserving true positions but risking occlusion.
Contiguous cartogram
Distorts region boundaries themselves so each area is proportional to data, keeping regions connected but producing strange shapes.
// 10 — FAQs
Frequently asked questions
What is a dorling cartogram?+
A Dorling cartogram is a type of cartogram that replaces geographic regions (countries, states, districts) with non-overlapping circles. Each circle's area is proportional to a data variable — such as population, GDP, or election votes — rather than the region's land area.
When should you use a dorling cartogram?+
Use a dorling cartogram when you want to compare quantities across regions without geographic size bias. It also works well when population, GDP, or vote counts need honest visual weight on a map, and when your audience is familiar with the general geography so circles still make sense.
When should you avoid a dorling cartogram?+
Avoid a dorling cartogram when precise geographic boundaries or shapes are critical to the analysis. It is also a poor fit when your audience is unfamiliar with the underlying geography, or when you have very many regions (hundreds) — the layout becomes a packed mess.
Is a dorling cartogram suitable for dashboards?+
Yes — a dorling 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 dorling cartogram?+
Dorling 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 dorling 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.