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Population Cartogram of California: A Century of Growth

August 14, 2009

I’ve had the opportunity to return to a particularly enjoyable map project during my studies at San Jose State.  This post exhibits the first installment of a cartogram of California completed May 2008, including a brief write-up I prepared earlier this spring for a wall display describing the project. I would later animate this cartogram using Flash, and I hope to post the animated version soon, but in the meantime, my friend John U has been kind enough to feature it on his blog.  You can find that post here.

JCoolidge_CalPopulationbyCo

The cartographer Borden Dent describes cartograms as thematic maps that “are drawn so that the areas of internal enumeration units are proportional to the data they represent” (1996, 203).  In a cartogram depicting population, the greater the number of people that live in a particular area, the larger that area appears on the map.  Cartograms of the fifty United States and the nations of the world are more common, but cartograms depicting counties are seldom implemented.

This series of cartograms pushes the limits of the medium, as the shapes of counties are less recognizable than those of states.  Still, I was determined to pursue an antidote to the “San Bernardino effect,” in which the magnitude of phenomena occurring in this particularly large county can be over-amplified using a choropleth technique.  I also sought to depict change over the course of the twentieth century, constructing six cartograms that each represent a twenty-year interval.

I exported a shapefile of California counties acquired from CaSIL out of ArcMap to Adobe Illustrator and manipulated the polygon sizes manually, tweaking them until a rough fit was achieved.  The result is a semi-contiguous cartogram with an aesthetic that references the cartograms of the 1970s and 1980s that originally inspired me.

Dent, B.D. (1996). Cartography: Thematic Map Design. 4th Ed. Dubuque, Iowa: Wm. C. Brown Publishers.

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