jkerski-esristaff

Creating Cartograms in ArcGIS

Blog Post created by jkerski-esristaff Employee on Feb 25, 2016
Cartograms, because they distort our expected view of mapped variables, are wonderfully rich tools for teaching and research.  They allow us to see relationships and trends that may not be evident in a typical choropleth map.  A distance cartogram shows relative travel times and directions within a network.  More common is an area cartogram, a map in which some variable is used instead of the land area in each polygon to determine the size of that polygon. I remember using graph paper to make rectangular area cartograms as an undergraduate (though I realize I am dating myself).  Today, one can use Web GIS and desktop GIS to create cartograms. For example, nearly 700 variables can be mapped on www.worldmapper.org, and the data can be downloaded as Excel spreadsheets and analyzed within ArcGIS.

Let's say you wanted to dig deeper and make your own cartograms, with the ability to do further analysis within a GIS environment.  You can use the cartogram geoprocessing tool that my colleague Tom Gross at Esri created.  How can a GIS, which focuses on accurate spatial representations of features, be used to create cartograms? Download the tool and find out!  The tool also includes step-by-step instructions and a sample set of data.

Once you install the cartogram tool, you simply run it to create the cartograms.  An intuitive interface allows specifying input and output.  You can even distort your base layers (such as the imagery shown below) so that your cartogram can include these as reference layers.  I did this for cities, a 30-degree world grid, and a satellite image of the Earth to see these reference layers overlaid on my cartogram.

In this example, I chose to map the 2015 population by country.  Then, I mapped the total CO2 emissions by country in 2004, in millions of metric tons, from the US Energy Information Agency. What patterns do you notice?

The cartogram map layer has to be written into a geodatabase, but otherwise, the tool has few restrictions. I am very pleased cartographically with the results, and the methodology of how these cartograms are generated is well documented:   These are Density-Equalizing Cartograms using methodology developed by Mark Newman and Michael Gastner at the University of Michigan.

What other variables and at what other scales could you map and analyze as cartograms?
pop_2015_cartogram1.jpg

Cartogram of World Population in 2015.

co2_cartogram_with_gdp.jpg

Cartogram of C02 emissions in 2004, as a Map Layout.

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