Walt and I were looking at the county-by-county electoral map on November 6, and saw that curving blue line across the deep south. I said, “What the hell is that? It’s got to be some kind of geographic feature.” We looked in Google Earth and didn’t see anything obvious, and then I got an idea and googled “Cotton Production 1860″. Voila, the maps match perfectly. I cropped the national electoral map to match the cotton map and put them both up on a page that very afternoon.
See this post on Wonkette, titled “Slaves vote heavily in Obama’s favor?“ Wonkette got it from Andrew Sullivan, who got it from Strange Maps, who got it from Pin the Tail, who apparently got it from me and posted it a week after my page went up.
Update: After this post went up, both Strange Maps and The Vigorous North cited my original post. They also add considerable interesting content, and The Vigorous North traces the landforms and soil types responsible for this pattern back to the late Cretaceous shoreline. Worth a look.
Update to the Update: Now featured on Rachel Maddow’s blog as part of an even more comprehensive discussion.