Visualizing Texas political drift 2008-2012

I always enjoy the maps and other data features at the Texas Tribune, but sometimes they inspire me to try to improve them.

A case in point is the Tribune’s recent map of party “drift” or Democratic-Republican change between the 2008 and 2012 presidential elections.

The Tribune map strikingly shows that Obama got fewer votes in 2012 than in 2008 in most Texas counties, but it made me wonder about the significance of the change, both as a percentage of votes cast and in terms of the population of each county.

A couple of approaches to adding more information to the map come to mind. The most obvious would be to use more shades to show percentage change. Another would be to use a cartogram, or a map where political units are resized according to population, like the famous election results cartograms of Mark Newman.

US presidential election results 2012, cartogram at county level by Mark Newman

But I don’t have easy access to cartogram software. So I cooked up the poor folks’ alternative to a cartogram: an Excel bubble chart (click for full size).

Texas political drift by county, 2008-2012

What can we see in this map? First, it supports the Tribune’s thesis that most Texas counties had Republican gains in 2012, at least in terms of presidential counts. However, it calls into question how significant the change was, for both Republicans and Democrats. None of Texas’ most populous counties experienced over 3% change, and in the three largest the change was less than 1%. Only a few tiny counties have the bright red indicating Republican gains over 6%. On the other hand, the Democrats have no bright blue counties, and most of the pockets where the Tribune showed Democratic gains turned out to be either under 1% change or in counties so small that they can barely be seen. The only notable blue on the map is in the Valley, and the only county of a significant size that broke 3% growth for the Democrats was Webb County (Laredo).

My map has plenty of room for improvement: the convention of the red-blue political scale makes light blue hard to distinguish from neutral gray, and keeping the circles small enough that Harris County doesn’t swallow the whole Houston area turns most West Texas counties into barely perceptible dots. Using Excel rather than a proper GIS means the map is missing some cartographic niceties: the projection is distorted, and it lacks an outline of the state that would make it a lot easier to recognize as Texas. Finally, while my data ranges and scales seem reasonable to me, it would be better to base them on some measure of statistical significance.

Nevertheless it’s a start. If you’d like to see my data sources or check my work, here’s the spreadsheet: texas-drift-2008-2012.xlsx.

Wireless usage in Austin public libraries

Preview of a paper I’m writing for my GIS class.

This map shows wireless sessions in proportion to “wireful” Internet terminal sessions at Austin Public Library branches. The regions on the map relate to the spatial analysis part of the paper: I’ve aggregated census block groups to the nearest library so I can estimate income and demographic characteristics for each branch.

Austin wireless map

My hypothesis is that people in the more affluent parts of town are better prepared to take advantage of the availability of public wireless in Austin. Libraries are a good place to study that because they’re open to everyone and because I could get wireful session counts with which to normalize the wireless counts.

I think this map roughly supports my hypothesis, although interestingly Oak Springs and Ruiz show wireless use more like westside libraries. Can anyone think of anything unusual about those branches to explain their high wireless rates? ACC and/or Riverside student apartments might do it for Ruiz, I suppose.

Meanwhile at Yarborough the wireless count is a full 22% of the wireful count! The next highest is barely over half that, at Old Quarry. Yarborough is my neighborhood branch and there’s nothing obvious to explain it. I’m seriously wondering whether someone in the adjacent apartment complex has a Pringles antenna. :-)