Yes, a cartogram is a type of thematic map. In cartography, maps fall into two broad categories: reference maps and thematic maps. Reference maps show locations, boundaries, roads, and place names. Thematic maps visualize data about a specific topic, like population density, income levels, or election results. A cartogram fits squarely in the thematic category because its entire purpose is to represent a data variable visually.
What Makes a Map Thematic
A thematic map focuses on the spatial pattern of a specific subject rather than simply showing where things are. A reference map of the United States, for example, shows state boundaries, highways, rivers, and city names. A thematic map of the United States might color each state by median household income or place dots to represent the density of hospitals. The defining feature is that the map encodes data about a particular theme and uses visual techniques (color, size, pattern, shape) to make that data readable at a glance.
Cartograms sit alongside several other well-known thematic map types: choropleth maps (regions shaded by data value), dot density maps (dots representing counts), flow maps (lines of varying thickness showing movement of goods or people), isoline maps (contour-style lines connecting equal values), and heat maps (color gradients showing concentration). Each technique visualizes one or two variables across geographic space, and each qualifies as thematic.
How Cartograms Work
What sets a cartogram apart from other thematic maps is its method: instead of adding colors or symbols on top of a normal map, a cartogram distorts the map itself. The size of each geographic unit (a country, state, or county) grows or shrinks in proportion to a chosen variable. A state with a large population appears physically larger on the map, while a sparsely populated state shrinks, regardless of how much land it actually covers.
This distortion is the cartogram’s core feature and its greatest strength. On a standard map, Russia dwarfs most of Europe, which can give the visual impression that Russia dominates any variable being shown. A cartogram sized by GDP, however, would shrink Russia considerably and enlarge countries like Germany or the United Kingdom, immediately communicating the economic reality in a way that a color-coded map might not.
Types of Cartograms
There are a few common variants. In a contiguous cartogram, regions stay connected to their neighbors but their shapes stretch and compress to reflect the data. This preserves the general layout of the map but produces unfamiliar, sometimes blob-like shapes. In a non-contiguous cartogram, each region keeps its recognizable outline but is scaled up or down and allowed to float free from its neighbors. You can still identify individual states or countries, but gaps appear between them.
A third type, the distance cartogram, is less about area and more about travel time or connectivity. Subway maps are a familiar example: they show stations and routes in a simplified layout without worrying about actual geographic distance between stops.
What Cartograms Are Used For
Population is the most common variable mapped with cartograms, but the technique works for any countable quantity. Researchers have used cartograms to visualize GDP, electoral college votes in U.S. presidential elections, child mortality rates, educational attainment, and obesity prevalence across states. The Worldmapper project, one of the best-known cartogram collections, generated maps of dozens of global variables, revealing stark inequalities between countries and regions that standard maps tend to hide.
A study published in PMC used density-equalizing cartograms to show state-level obesity trends in the United States from 1996 to 2006. By resizing states according to population and educational attainment, the researchers produced maps that gave health policymakers a clearer picture of where obesity was concentrated in human terms, not just geographic terms. A large, sparsely populated state no longer dominated the visual simply because it covered a lot of land.
Cartograms vs. Choropleth Maps
The most direct comparison is between a cartogram and a choropleth map, since both are thematic maps designed to show how a variable differs across regions. A choropleth uses color shading on a geographically accurate map. A cartogram distorts area to encode the data directly into the map’s geometry.
Choropleth maps have a well-known weakness: large, low-population regions can dominate the visual and skew a viewer’s perception. A choropleth of U.S. election results, for instance, fills the screen with the color of whichever party wins rural western states, even though relatively few voters live there. A cartogram sized by population (or electoral votes) corrects this by making densely populated areas visually prominent.
The tradeoff is legibility. Cartograms distort familiar shapes, which can confuse readers who aren’t used to the technique. A contiguous cartogram of Europe may be unrecognizable at first glance. Audiences often need a moment of orientation, and sometimes a legend or explanatory note, before the map clicks. Choropleth maps, by contrast, look like the maps people already know, making them easier to read immediately even if they carry that built-in bias toward large regions.
Why the Classification Matters
Understanding that a cartogram is a thematic map helps you choose the right tool for the job. If your goal is to show where places are, you need a reference map. If your goal is to show how a variable like wealth, health outcomes, or population is distributed across space, you need a thematic map, and a cartogram is one of several options. It works best when the physical size of regions actively misleads viewers about the data, such as when small, dense places carry outsized importance for the variable you’re mapping. In those situations, no other thematic map type communicates the disparity as immediately as a cartogram does.