Choropleth Maps of Presidential Voting

November 1, 2010

(This article was first published on David B. Sparks » r, and kindly contributed to R-bloggers)

Having always appreciated the red and blue cartograms and cartographs of geographic electoral preferences, such as those made available by Mark Newman, I sought to produce similar maps, but include information about support for non-“state-sponsored” parties, and to extend the coverage back in time.

I was able to find county-level presidential election returns going as far back as 1920, thanks to the CQ Press Voting and Elections Collection (gated). I converted the proportion of the vote garnered by Democratic, Republican, and “Other” parties’ candidates to coordinates in three-dimensional RGB color space, and used shapefiles from the mapdata package to plot these results as choropleth maps with ggplot.

Click to view slideshow.

It is interesting to observe these maps in a series, which gives historical context to the Red State/Blue State narrative. Most obviously, there is a significant shift in the geographic center of Democratic support, from a concentration in the southeast to the present equilibrium, localized on each coast and near the Great Lakes.

Among these 23 elections, landslide victories, such as Roosevelt over Landon in 1936, Johnson over Goldwater in 1964, Nixon over McGovern in 1972, and Reagan over Mondale in 1984, tend to stand out for their monochromaticity.

Also intriguing are the elections featuring substantial support for third-party candidates. Most of these are individuals who were had a strong support base in a specific region of the country, such as La Follette in the northwest, and Thurmond and Wallace in the deep south. Ross Perot’s run in 1992 is unique here, as his relatively broad geographic base of support results in a map that runs the gamut to a greater degree than any others.

Click on the image below to see a full screen version of the slideshow above, or to download any of the individual maps as PNGs.

Goldwater Click for slideshow/download

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