"Historian Susan Schulten writes in her book Mapping the Nation: History and Cartography in Nineteenth-Century America that during the 1850s many abolitionists used maps to show slavery's historical development and to illustrate political divisions within the South. (You can see many of those maps on the book’s companion website.) Schulten writes that President Lincoln referred to this particular map often, using it to understand how the progress of emancipation might affect Union troops on the ground. The map (hi-res) even appears in the familiar Francis Bicknell Carpenter portrait First Reading of the Emancipation Proclamation of President Lincoln, visible leaning against a wall in the lower right-hand corner of the room."
Via Seth Dixon