Especially as it pertains to Arkansas. I'm surprised there were any slaves at all in Newton, Searcy, Carroll, and Madison counties, which are all in the Ozarks. The only Arkansas state legislator who voted not to secede in 1861 was from Madison County.
It's also interesting to see how county boundaries have changed, and how new ones were added after that map was made. After the Civil War, Arkansas got Grant and Lincoln counties, and to offset those, I guess, a Lee County as well. There was also a new county added called Baxter, in honor of the Reconstruction governor who was Arkansas's last Republican governor until Winthrop Rockefeller was elected in 1966.