One of the main reasons Republicans have a big advantage on the congressional map in the years ahead has nothing to do with politicians gerrymandering districts; it has to do with Americans gerrymandering themselves.
Basically, the argument (which I have espoused) is that Republicans have an advantage when it comes to map-making because their voters are much more diffuse and spread out, while Democratic voters tend to be more concentrated in urban areas. So while Republicans have a bunch of districts that they generally win with 55 or 60 percent, Democrats have many more districts that are 70 percent-plus Democratic performing.
Thus, the half of Americans who tend to favor Democrats are concentrated in fewer districts, leaving Republicans with many more districts -- and states -- that lean their way.
One point of contention on this theory, though, is the "why." Why are Americans sorting themselves in this way? Are people who just happen to live in more rural areas simply drawn to the Republican Party and city-dwellers to Democrats, or are Republicans actually physically moving away from the cities so they can live near people who agree with them politically (and vice versa for Democrats)?
Well, according to new data from the Pew Research Center, it's pretty clear that politics do inform people's decisions when they move -- to a significant extent.
The data show that 77 percent of people who are "consistently liberal" favor urban communities, while 75 percent of "consistent conservatives" favor a more spacious lifestyle. And there's a pretty smooth progression as you move along the political continuum between the two.