It isn’t often that a map visually displays a moral issue facing a divided nation and then affects a President’s response. Yet nearly 150 years ago, the U.S. Coast Survey — NOAA’s predecessor organization — produced such a map that, according to historians, President Abraham Lincoln used to coordinate military operations with his emancipationpolicies.

Created in September 1861, the map entitled “Map showing the distribution of the slave population of the southern states and the United States” is based on statistics from the eighth Census. It is included in NOAA’s new specialcollection of Civil War maps and charts, “Charting a More Perfect Union,” which contains over 400 documents gathered in one place to mark the 150th anniversary of the Civil War.

“The map was among the first to use shading to represent the human population,” explains retired NOAA CorpsCapt. Albert Theberge, the chief of reference for the NOAA Central Library. “It is a prime example of how Coast Survey science aided the Union cause during the Civil War.”

In addition to initiating a trend of statistical cartography, the map’s thematic display of “moral statistics” was revolutionary in affecting political change.

Northern audiences were able to see that the first states to secede were those with the most slaves. Usingshading to represent the human population, the darkest areas of the maps show the highest density slave populations, and the order of secession corresponds closely to the shade densities of the map. Moreover, a table in the corner of the map shows the number of slaves in each state and the proportion of slaves to the total population.

The 1860 Census was supervised by Joseph Camp Griffith Kennedy who had wanted to include slaves by name in the U.S. Census Report, but Congress refused. Alexander D. Bache was the U.S. Coast Survey superintendent at the time, and the map was created under Edwin Hergesheimer, a cartographer with U.S. Coast Survey’s drawing division.

It was Francis Bicknell Carpenter, painter of “First Reading of the Emancipation Proclamation of President Lincoln” in 1864, who first noticed that President Lincoln frequently consulted this map in considering the relationship between emancipation and military strategy. Carpenter had spent the first six months of 1864 in the White House preparing the portrait and noted 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. The Emancipation Proclamation became law on Jan. 1, 1863.

The NOAA connection to the map had been lost over the decades. John Cloud, Ph.D., a historian and NOAA employee who was recovering significant Coast Survey cartographic products in NOAA’s Climate Database Modernization Program, recently discovered the connection with Hergesheimer and the U.S. Coast Survey.

The Office of Coast Survey’s “Charting a More Perfect Union” project is supported by the NOAA Preserve America Initiative — part of a federal initiative to preserve, protect and promote our nation's rich heritage.