Mason–Dixon line
The Mason–Dixon line, sometimes referred to as Mason and Dixon's Line, is a demarcation line separating four U.S. states: Pennsylvania, Maryland, Delaware and West Virginia. It was surveyed between 1763 and 1767 by English surveyors and astronomers Charles Mason and Jeremiah Dixon as part of the resolution to Cresap's War, a border conflict involving Maryland, Pennsylvania, and Delaware (then a part of Pennsylvania) in colonial America.