According to the 1860 census the population of the United States was 31,429,891. Of that number, 3,952,838 were reported as enslaved. This landmark map, published by the U.S. Coast Survey in 1861, provided a graphic breakdown of those census returns, specifically focusing on percentage of slave population per county amongst the total population in the southern portion of the country. Shading from lower percentages per county in light grey to higher percentages illustrated in darker tones provides a dramatic representation of slavery in the southern states. This map was, by some accounts, consulted by Abraham Lincoln throughout the course of the Civil War.