Cartogram

TL;DR

• A cartogram distorts geographic region size and shape to encode a chosen statistical variable (for example, population or GDP).
• Larger regions on a cartogram indicate higher values of the represented variable; smaller regions indicate lower values.
• Useful for visual comparisons across places, but geography is deformed and interpretation can be more difficult than with traditional maps.

Definition

A cartogram is a type of map that uses a statistical variable, such as population or GDP, to distort the size and shape of geographic regions in order to better represent the variable of interest. The resulting map is a spatial representation of the variable, with larger regions indicating higher values and smaller regions indicating lower values.

Explanation

Cartograms map a chosen quantitative variable onto geographic regions by changing those regions’ apparent area and shape so that visual area corresponds to the variable’s value. This spatial distortion emphasizes differences in the variable across regions and can reveal patterns or trends that are less obvious on an undistorted, traditional map. Because regions are reshaped to reflect the data, a cartogram prioritizes the represented statistic over accurate geographic form.

Examples

Population cartogram

A population cartogram uses population data to distort the size and shape of geographic regions. For instance, a population cartogram of the United States would show larger states such as California and Texas as being significantly larger than smaller states such as Vermont and Wyoming, in order to accurately represent the relative population sizes of each state.

GDP cartogram

A GDP cartogram uses GDP data to distort the size and shape of geographic regions. For instance, a GDP cartogram of the world would show larger economies such as the United States and China as being significantly larger than smaller economies such as Zimbabwe and Nepal, in order to accurately represent the relative GDPs of each country.

Political power cartogram

A political power cartogram represents political influence or power. For instance, a political power cartogram of the European Union would show larger countries such as Germany and France as being significantly larger than smaller countries such as Malta and Luxembourg, in order to accurately represent the relative political power of each country within the EU.

Environmental impact cartogram

An environmental impact cartogram uses measures such as carbon emissions or deforestation to distort countries’ sizes. For instance, an environmental impact cartogram of the world would show countries with high levels of carbon emissions or deforestation as being significantly larger than countries with low levels of these environmental impacts, in order to accurately represent the relative environmental impact of each country.

Use cases

• Visualizing and comparing a statistical variable (for example, population, GDP, political power, or environmental impact) across different geographic regions.
• Highlighting patterns and trends in spatial data that may not be apparent on conventional maps.

Notes or pitfalls

• Cartograms distort geographic size and shape, so they do not accurately represent actual geography.
• They can be difficult to create and interpret, often requiring specialized software and a thorough understanding of the data and variable being represented.
• Because of their distortion, cartograms are best used alongside traditional maps to provide a complete and accurate representation of the information.

Related terms

• Statistical variable
• Population cartogram
• GDP cartogram
• Political power cartogram
• Environmental impact cartogram
• Traditional map