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november 07, 2004
Kartor över det amerikanska valet: Diffusion-based method for producing density equalizing maps
Michael Gastner, Cosma Shalizi, and Mark Newman: Maps and cartograms of 2004 US presidential election results visar och diskuterar olika typer av kartor för att representera resultet av det amerikanska valet. För fina bilder, se artikeln.
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. (Hawaii and Alaska are not shown on the map.) 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.
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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.
Algoritmen som nämns i artikeln finns i:
Michael T. Gastner, M. E. J. Newman: Diffusion-based method for producing density equalizing maps
Abstract:
Map makers have long searched for a way to construct cartograms -- maps in which the sizes of geographic regions such as countries or provinces appear in proportion to their population or some other analogous property. Such maps are invaluable for the representation of census results, election returns, disease incidence, and many other kinds of human data. Unfortunately, in order to scale regions and still have them fit together, one is normally forced to distort the regions' shapes, potentially resulting in maps that are difficult to read. Many methods for making cartograms have been proposed, some of them extremely complex, but all suffer either from this lack of readability or from other pathologies, like overlapping regions or strong dependence on the choice of coordinate axes. Here we present a new technique based on ideas borrowed from elementary physics that suffers none of these drawbacks. Our method is conceptually simple and produces useful, elegant, and easily readable maps. We illustrate the method with applications to the results of the 2000 US presidential election, lung cancer cases in the State of New York, and the geographical distribution of stories appearing in the news.
Via Cosma Shalizi (Three-Toed Sloth): Decided and Divided Americas
Posted by hakank at november 7, 2004 07:06 FM Posted to Statistik/data-analys