The Coast Survey map of slavery was one of many maps drawn from data produced in 19th-century America. As historian Susan Schulten has shown, this particular map was created by a federal government agency from statistics gathered by the Census. Abraham Lincoln consulted it throughout the Civil War. A banner on the map proclaims that it was "sold for the benefit of the Sick and Wounded Soldiers of the U.S. Army." The data map was an instrument of government, as well as a new technology for representing knowledge.
To help show the big patterns of American slavery, I have created an interactive map of the spread of slavery. Where the Coast Survey map showed one measure, the interactive map shows the population of slaves, of free African Americans, of all free people, and of the entire United States, as well as each of those measure in terms of population density and the percentage of the total population. The map extends from the first Census in 1790 to the Census taken in 1860 on the eve of the Civil War. You can explore the map for yourself, but below I have created animations to highlight some of the major patterns.
When looking at all of these maps together, it's noticable that even as the total number of enslaved peoples in the United States increased between 1790 and 1860, the multitudes were dispersed across the increasing expanse of the United States, rather than becoming more concentrated in areas where slavery was well established.
In counties along the Atlantic Coast in 1790 and 1800, the population of slaves at any one time was nearly at its peak. (This is all the more remarkable since many slaves fled to the British during the Revolutionary War.) Take for example, Charleston County, South Carolina. In 1790, almost 51,000 people were enslaved in that county. In 1840, the slave population reached its peak of nearly 59,000 people; by 1860, there were 37,000 enslaved people, just 63 percent as many slaves as two decades earlier.
The total number of slaves in the eastern seaboard states did, however, grow slowly over time, but not at anything like the rate of growth for free people in the North. The free white population in the North grew in already settled places and spread to the West.
The slave population had a different dynamic. It grew in intensity in places around the Chesapeake Bay, even as slavery was gradually abolished in the North. But for the most part the slave population spread westward to the lands opened for settlement by the Louisiana Purchase, the dispossession of the Indian nations of the Southeast, the war with Mexico, and the distribution of public lands. Slavery spread rather than grew because it was an agricultural rather than industrial form of capitalism, so it needed new lands.
And slavery spread because enslaved African Americans were forced to migrate. Historian Steven Deyle estimates "that between 1820 and 1860 at least 875,000 American slaves were forcibly removed from the Upper South to the Lower South." A minority of that migration happened because white planters migrated along with the people that they owned. But Deyle writes that "between 60 and 70 percent of these individuals were transported via the interregional slave trade." In other words, slavery was not the paternalist institution that its apologists made it out to be: it was an relentlessly exploitative system where the fundamental relation of owner to enslaved was defined by the markets. The unceasing spread of slavery provoked political crises, eventually leading to the Civil War. As Abraham Lincoln put it in is 1858 "House Divided" speech:
"Either the opponents of slavery, will arrest the further spread of it, and place it where the public mind shall rest in the belief that it is in the course of ultimate extinction; or its advocates will push it forward, till it shall become alike lawful in all the States, old as well as new, North as well as South."
Below you can see two animations comparing the density of the slave population and the density of the total population (keep in mind that the scales are different).
This animation of the density of slave population from 1790 to 1860 shows how slavery expanded more than it grew.
This animation shows the percentage of the population enslaved from 1790 to 1860.
Susan Schulten, Mapping the Nation: History and Cartography in Nineteenth-Century America (Chicago: University of Chicago Press, 2012), writes about maps of slavery in chapter 4; see also the book's companion website which offers images of maps of slavery. Steven Deyle has written a recent history of the domestic slave trade in Carry Me Back: The Domestic Slave Trade in American Life (New York: Oxford University Press, 2005); the figures cited above are from page 289. Of the many excellent histories of American slavery, see one of these: on the settlement of the Mississippi River valley, Walter Johnson, River of Dark Dreams: Slavery and Empire in the Cotton Kingdom (Cambridge, Belknap Press of Harvard University Press, 2013); on the life of slaves, Erskine Clarke, Dwelling Place: A Plantation Epic (New Haven: Yale University Press, 2005); on the history of slavery generally, Ira Berlin, Generations of Captivity: A History of African-American Slaves (Cambridge, MA: Belknap Press of Harvard University Press, 2003).
The data in my maps is drawn from the 1790 to 1860 Censuses compiled by the Minnesota Population Center, [National Historical Geographic Information System], version 2.0 (Minneapolis: University of Minnesota, 2011).
Source: smithsonian.com By Lincoln Mullen