Wednesday, 22 February 2012

The Dorling Cartogram

My last project involved using a multitude of regions for drawing analysis, parallels and comparison. Not wanting to use yet another Choropleth graph, I decided to look up alternatives which were easier to create and preferably required no VBA.

Soon I stumbled upon "The Dorling Cartogram", defined in the UCSB site as, "This type of cartogram was named after its inventor, Danny Dorling of the University of Leeds. A Dorling cartogram maintains neither shape, topology nor object centroids, though it has proven to be a very effective cartogram method. To create a Dorling cartogram, instead of enlarging or shrinking the objects themselves, the cartographer will replace the objects with a uniform shape, usually a circle, of the appropriate size."

I had the data for Obesity in the United States handy, so I decided to give it a try before using it in my project. I opted to use Bubble charts because data points within a series may need to be of varied shapes based on its obese population while the colors indicated different tiers of obesity percentage. Thus larger the circle and redder it is, the severe the obesity. To determine the obese population per state, I have used 1990 Census data to calculate between 1995-2000 and the 2000 Census data to calculate between 2001-2010.

My version of Dorling Cartogram in Excel:

Parting words: As Dorling Cartograms are non-overlapping. In places they overlapped, it is common practice they rather be moved so that the full area of each shape can be seen. The positions of several states in relation to each other are hence slightly altered as per this principle.

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