It’s arguably the most important map in our country’s history. After the Revolutionary War, British and American representatives met in Paris to negotiate the boundaries of a new nation: the United States of America. Both sides had a version of the same map, marked up to indicate where they thought the lines should be drawn.

“The diplomats literally debated the boundaries of the future United States while pointing at this map,” says Matthew Edney, a historian of cartography at the University of Southern Maine. Although the 1783 Treaty of Paris contains no maps or illustrations, its written descriptions of boundaries are based on the marked-up maps of the negotiators, Edney says.

The map used as a starting point by both sides was created