On election night on national telecasts, all the American public kept seeing on maps of the vote was a "sea of red". Most of us geographers and GIS folks knew otherwise, and found ourselves hoping for some more accurate cartographic renderings of the true vote. Here is a great article that looks into various methods to accurately report them.
Maps and cartograms of 2004 US presidential election results
Michael Gastner, Cosma Shalizi, and Mark Newman University of Michigan
On election night and in the days since then, we have seen many maps that look like this:
The states of the country are colored red or blue to indicate whether a majority of their voters voted for the Republican candidate (George W. Bush) or the Democratic candidate (John F. Kerry) respectively. The map gives the superficial impression that the "red states" dominate the country, since they cover far more area than the blue ones. However, as pointed out by many others, this is misleading because it fails to take into account the fact that most of the red states have small populations, whereas most of the blue states have large ones. The blue may be small in area, but they are large in terms of numbers of people, which is what matters in an election.
We can correct for this by making use of a cartogram, a map in which the sizes of states have been rescaled according to their population. That is, states are drawn with a size proportional not to their sheer topographic acreage -- which has little to do with politics -- but to the number of their inhabitants, states with more people appearing larger than states with fewer, regardless of their actual area on the ground. Thus, on such a map, the state of Rhode Island, with its 1.1 million inhabitants, would appear about twice the size of Wyoming, which has half a million, even though Wyoming has 60 times the acreage of Rhode Island.
Here are the 2004 presidential election results on a population cartogram of this type:
The cartogram was made using the diffusion method of Gastner and Newman, which is described in detail in this article. Population data were taken from the 2000 US Census. Iowa and New Mexico, which at the time of writing were officially undeclared, we have assumed to have a Republican majority -- all indications are that this will be the final declaration once recounts are complete.
The cartogram reveals what we know already from the news: that the country was actually very evenly divided by the vote, rather than being dominated by one side or the other.
But we can go further. We can do the same thing also with the county-level election results and the images are even more striking. Here is a map of US counties, again colored red and blue to indicate Republican and Democratic majorities respectively:
Similar maps have appeared in the press, for example in USA Today, and have been used as evidence that the Republican party has wide support. Again, however, a cartogram gives a more accurate picture. Here is what the cartogram looks like for the county-level election returns:
Again, the blue areas are much magnified, and areas of blue and red are now nearly equal. However, there is in fact still more red than blue on this map, even after allowing for population sizes. Of course, we know that nationwide the percentages of voters voting for either candidate were almost identical, so what is going on here?
The answer seems to be that the amount of red on the map is skewed because there are a lot of counties in which only a slim majority voted Republican. One possible way to allow for this on a map, suggested by Robert Vanderbei at Princeton University, is to use not just two colors, red and blue, but instead to use red, blue, and shades of purple to indicate percentages of voters. Here is what the normal map looks like if you do this:
And here's what the cartogram looks like:
In this map, the red counties occupy only a rather small portion of the total area, most of the country appearing either in blue or in shades of purple.
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On election night on national telecasts, all the American public kept seeing on maps of the vote was a "sea of red". Most of us geographers and GIS folks knew otherwise, and found ourselves hoping for some more accurate cartographic renderings of the true vote. Here is a great article that looks into various methods to accurately report them.
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