Geodemographics of Slavery Before the US Civil War

I was just made aware of a very cool map of the pre-Civil War slave population of the southern states in the United States that is posted to the New York Times website. If you haven't seen it already, you must visit it, since it has considerable historical importance:

We don’t know when Lincoln first encountered the Coast Survey’s map of slavery. But he became so taken with it that Francis Bicknell Carpenter included it in the lower right corner of his painting, “President Lincoln Reading the Emancipation Proclamation to His Cabinet.” Carpenter spent the first six months of 1864 in the White House preparing the portrait, and on more than one occasion found Lincoln poring over the map. Though the president had abundant maps at his disposal, only this one allowed him to focus on the Confederacy’s greatest asset: its labor system. After January 1, 1863—when the Emancipation Proclamation became law—the president could use the map to follow Union troops as they liberated slaves and destabilized the rebellion.

We use GIS these days to create maps like this, and can do such maps in a very short amount of time because of the readily availability of data, but that was a very different story a century and a half ago. This map uses data from the 1860 census and was drawn up by the US Coastal Survey.