Old maps are being made available for the first time online. They are from a series called 'Mapping the Nation' collected by Charles O'Paullin, Over 700 maps were published in 1932 in O'Paullin's Atlas of the Historical Geography of the United States. They all now have been put online for the public.
These maps from are basically 'census' maps showing the location and numbers of slaves.
You can click on these maps to make them larger and easier to read.