One image did more to end slavery in the United States than any other. It was the map through which Abraham Lincoln saw slavery, and it changed the way he thought about the Civil War.
President Lincoln’s map of slavery was the 1861 U.S. Coast Survey Map. It drew on census data and used groundbreaking cartographic techniques for the era to visually depict the four million Americans held in bondage in the Southern states. The map revealed which counties had the highest concentrations of slaves, as well as which parts of the Confederacy might be the least committed to the institution.
Lincoln relied on this snapshot map of slavery before the Civil War to decide how to propose abolition. The map pushed him to issue the Emancipation Proclamation, and it drove Union support for ending slavery during the darkest days of the Civil War.
In 1860, President-elect Lincoln had not even been sworn into office before a wave of Southern states began to secede from the Union. First, South Carolina seceded on December 20, 1860, followed in January by Mississippi, Florida, and Alabama. By the time Lincoln was inaugurated on March 4, 1861, seven states had vowed to leave the United States over the issue of slavery.
In his first inaugural address, Lincoln declared, “I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists.” But as time wore on, one map would play a large role in changing Lincoln’s mind.
This map, produced by the US Coast Survey in 1861, drew on census reports from 1860, the final year the United States government collected census data on slaves. The map shows the prevalence of slavery by county, with darker counties representing a higher percentage of slaves and lighter counties a lower percentage.
The map was visual proof of the South’s dependence on slave labor. It also gave the public a way to visualize the variations of slavery throughout the South during the Civil War. More importantly, President Abraham Lincoln relied on the map in deciding how to end the institution of slavery.
The US Coast Survey was largely responsible for mapping US coastlines and waterways—in fact, the act that created the agency, signed in 1807 by President Thomas Jefferson, was called "An Act to provide for surveying the coasts of the United States."
Creating a slavery map was not exactly in the agency’s job description, but that did not stop the US Coast Survey from producing a groundbreaking map that shaped the course of the Civil War. The map relied on a new way to show population variations using shading. As the map explains, some counties “appear comparatively light” because of low slave populations, while other areas showed a high concentration of slaves.
The 1861 Coast Survey map showed that in some counties, more than 90% of the population was made up of slaves. Along the Mississippi River, slaves vastly outnumbered free whites. Many of these slaves may have reached the Deep South via the “slavery trail of tears,” which forced about a million slaves to walk a thousand miles from Virginia to cotton country.
Lincoln had seen these very slaves when he traveled the Mississippi River in 1828 and 1831, transporting farm goods to New Orleans. But the urban South had a much smaller percentage of slaves; for example, only 8.9% of the population in Orleans Parish, Louisiana, was made up of slaves. The rest of the city was largely comprised of whites and free blacks. These numbers on the Coast Survey map drove home the vastly different experiences of slavery in Confederate cities vs. those in rural and farming areas.