The Civil War started 150 years ago today.
Learn how the map shown above informed the military strategy to end slavery:
Commercial lithographer Henry S. Graham printed this choropleth map showing the distribution of the slave population in September 1861. The map shows in graphic terms the density of the slave population in the Southern states, based on figures from the 1860 census. Although the development of this map was a collaborative government effort, cartographers working for Edwin Hergesheimer, U.S. Coast Survey Drafting Division, created it.
The development of this map was revolutionary for its time for several reasons. First, it was among the first of its kind, initiating a trend of statistical cartography in the United States that allowed the thematic mapping of larger social, political, and cultural trends. Second, this map represented an early use of statistical information from the census. Third, new techniques in shading developed by Hergesheimer were a path-breaking application of these new techniques to human geography. Finally, its makers went as far to use “moral statistics” in order to affect political change.
The map was created to understand the secession crisis, by providing a visual link between secession and slavery. The mapmakers consciously limited the map to just the Southern states, including the Border States of Maryland, Virginia, and Kentucky, but not the Western slave states of Nebraska, New Mexico, and Utah. During and after the war, the map then could be used by the Union to argue that the destruction of the Confederacy meant the destruction of slavery. There is a strong message in the banner at the top of the map that reads “For the Sick and Wounded Soldiers of the U.S. Army.”
According to artist Francis Bicknell Carpenter, this map was frequently consulted by President Abraham Lincoln in considering the relationship between emancipation and military strategy. Carpenter took up residence at the White House in February 1864 to paint President Lincoln, after he was inspired by Lincoln’s Emancipation Proclamation. Carpenter wrote that Lincoln would look at the map and send his armies to free blacks in some of the highest density areas in order to destabilize Southern order.