This is from Strange Maps (no big surprise there).
The first map shows the counties throughout the South that voted for Barack Obama. The darker blue the higher the vote.
The second map shows the centers of cotton production in 1860, immediately before the Civil War. Saying "cotton production" is obviously an alternate here for pinpointing centers of dense African-American population in the 19th Century.
If you go to StrangeMaps you can find out what happens when you superimpose the two. I'm not going to steal that, because he did the work and you should take the 30 seconds to visit his site.
As a historian what fascinates me most is the apparently static nature of concentrations of African-American populations in the South. It says something--even in the year we have just elected the first black President--about the relative failure of an informal pattern of de facto segregation to dissipate, even after nearly 150 years.
As a political animal, it tells me that the real level of analysis is the county and not the state level.
But I have to admit, when I saw the superimposed maps, the first thing that happened was that a chill ran up my spine [not to be confused with a tingle running down Chris Matthews' leg].