A cartogram is a map that changes the size of places to show data instead of true land area. This makes patterns easier to see when the data is more important than physical shape, such as population, income, energy use, or election results. A country with a large data value appears larger, while a country with a small data value appears smaller.
Cartograms matter because they help students compare places quickly and notice global inequalities that a regular map can hide.
In a cartogram, location and shape are often simplified so the map can communicate one main variable clearly. For example, a world population cartogram makes India and China very large because they have huge populations, while countries with large land area but fewer people, such as Canada or Australia, shrink. Good cartograms still use labels, legends, colors, and familiar regional placement so readers can recognize places.
The key skill is to read size as data, not as land area.
Understanding Maps & Geography Skills: Cartograms
Cartograms are built by linking each place to a number in a data table. The map maker chooses a rule that turns that number into visual area. This is important because people tend to judge the size of a shape by its area, not by its height or width alone.
If a value becomes four times larger, the displayed area should become four times larger. The shape cannot simply be stretched in one direction.
Doing that would make the visual comparison misleading. Computer programs often move borders many times until each region reaches an area close to its target value.
Different cartogram designs make different compromises. A contiguous cartogram keeps neighbouring places connected, but borders can become very bent and hard to recognise. A noncontiguous cartogram allows gaps between places.
It can preserve each place's general outline more clearly, though the gaps no longer represent real distance. A Dorling cartogram replaces areas with circles of different sizes. These circles do not overlap and usually stay near their real locations.
This version is good for comparing totals, but it hides the exact borders of countries or districts. Students should identify the design before drawing conclusions from the map.
The most important reading skill is checking whether the map shows totals or rates. A total population map gives large countries an advantage because more people live there. A map of doctors per person, disease cases per one hundred thousand people, or carbon emissions per person answers a different question.
A small country can have a high rate while remaining small on a total-value cartogram. This distinction appears in news reports about elections, public health, wealth, and climate change.
A map of total votes shows where many voters live. A map of vote share shows how strongly a party was supported in each place.
Cartograms can make a pattern memorable, but they can hide details. A region may look large because of a large total, even when the average person there has a low value. Very small places may be difficult to label or may disappear entirely.
Data from different years can create a false comparison if this is not stated. The choice of colours matters too. Darker colour may represent a second variable, such as a rate, while size represents a total.
Read the title, date, source, unit, and legend before interpreting the shapes. Compare the cartogram with a regular map when location, distance, borders, or land area matter to the explanation.
Key Facts
- A cartogram resizes places based on a data value rather than true land area.
- Cartogram size rule: larger symbol area means larger data value.
- Example: If Country A has twice the population of Country B, it may be drawn with about twice the area.
- Cartograms are useful for population, GDP, carbon emissions, disease cases, election votes, and resource use.
- A legend or scale is needed because the map size represents data units, such as people, dollars, or tons of CO2.
- Cartograms trade geographic accuracy for clearer data comparison.
Vocabulary
- Cartogram
- A map that changes the size or shape of places to represent a data value.
- Data value
- A measured amount used to compare places, such as population, income, or emissions.
- Distortion
- A change in a map's shape, size, distance, or direction from real-world geography.
- Legend
- A map key that explains the meaning of colors, symbols, sizes, or categories.
- Proportional area
- A map design rule where the area of a shape matches the relative size of a data value.
Common Mistakes to Avoid
- Reading cartogram size as land area is wrong because the resized shapes represent data values, not physical territory.
- Ignoring the legend is wrong because the map cannot be interpreted accurately without knowing what variable and units the sizes show.
- Comparing only shape instead of area is wrong because cartograms usually encode data by total area, not by width, height, or outline alone.
- Assuming distorted places are misplaced is wrong because cartograms often keep only approximate location to make the data pattern easier to see.
Practice Questions
- 1 A cartogram uses 1 square centimeter to represent 10 million people. How large should a country with 80 million people be drawn?
- 2 Country X has a GDP of 2 trillion dollars and Country Y has a GDP of 500 billion dollars. If Country Y is drawn with an area of 3 square centimeters, what area should Country X have on a proportional cartogram?
- 3 A land-area map makes Canada look much larger than India, but a population cartogram makes India much larger than Canada. Explain what this tells you about the difference between land area and population.