Over the next few months, I’ll be posting maps to set up the geographical context of the 2008 presidential election, and to explain how I came up with the 10 Regions of American Politics. Today’s map (click to get a larger view) shows how much the two parties’ bases have changed since Ronald Reagan was elected in 1980 — that is, during the quarter century in which conservative Republicanism dominated American politics. As it happens, the GOP share of the vote in 1980 and in 2004, when George W. Bush was elected to a second term, was almost exactly the same (50.75 percent for Reagan, 50.73 percent for Bush), which makes for a handy comparison.

As the map shows, the Republican Party has become more dependent on the South and on rural areas since Reagan (a Western suburbanite) was its leader. Georgia and Louisiana are much more Republican than when Jimmy Carter was the Democratic nominee, but you can see specks of blue (representing a GOP slide) in Atlanta and New Orleans. And even Texas has a light blue island (Dallas) in a sea of red. Conversely, in the north, Oregon has become more Democratic thanks to the Portland area, but the rural counties in the east of the state have actually become more solid for the GOP.

Stay tuned for close-up maps breaking down the changes in party share by region. For now, you can also view more detailed version of the above map, including county lines, by clicking on the thumbnails below.

R_share_of_vote_198004_northeast_3 R_share_of_vote_198004_southeast_3 R_share_of_vote_198004_midwest_2 R_share_of_vote_198004_northwest_2 R_share_of_vote_198004_southwest_2