Surveyed 1763–1767 · PA–MD border at about 39°43′N · about 233 miles · North–South symbol
Mason–Dixon Line map
The Mason–Dixon Line is the border between Pennsylvania and Maryland, with the Delaware boundaries attached, surveyed by Charles Mason and Jeremiah Dixon between 1763 and 1767. It later came to stand for the division between North and South.
Where the line is
The main line is the east–west border between Pennsylvania and Maryland, on the parallel of about 39°43′20″N. It runs from the northeast corner of Maryland, near the Delaware line, west for about 233 miles, past the point where Maryland's western tip ends and the border continues along West Virginia's northern edge. Mason and Dixon also surveyed the north–south "tangent line" between Maryland and Delaware and part of the 12-mile arc around New Castle that gives Delaware its curved northern border. Together these lines fixed the shapes of three states.
Key facts
- Surveyors: Charles Mason, an astronomer, and Jeremiah Dixon, a surveyor, both from England, working from November 1763 to 1767.
- The dispute: the Penn family of Pennsylvania and the Calvert family of Maryland had argued over the border for 80 years, since their overlapping royal grants of 1632 and 1681. Philadelphia would have been in Maryland under the Calvert claim.
- Length: about 233 miles westward from the Maryland–Delaware corner; the survey stopped short of the full five degrees of longitude because Native nations refused passage beyond Dunkard Creek, near present-day Mount Morris. The remaining 30-odd miles were completed in 1784 and became the Pennsylvania–West Virginia line.
- Markers: limestone stones shipped from England were set every mile, with "crownstones" carrying the Penn and Calvert coats of arms every fifth mile; many survive.
- Pennsylvania's abolition of slavery in 1780 made the line the boundary between free and slave states in the East; the term "Mason–Dixon Line" was used in the Missouri Compromise debates of 1820 to mean the whole North–South divide, extended in the popular mind along the Ohio River.
Cities near the line
Philadelphia and Wilmington are just north of its eastern end; Baltimore is 40 miles south of it. Along the line itself are Hagerstown, Maryland, and Gettysburg, Chambersburg and Hanover, Pennsylvania; the Confederate army crossed the line north to Gettysburg in June 1863. Cumberland, Maryland, sits close to the western section, and Pittsburgh lies 50 miles north of the West Virginia segment. Harpers Ferry, where Maryland, Virginia and West Virginia meet at the Potomac, is 20 miles south of the line.
How the line shaped the map
The Pennsylvania–Maryland border is the reason Maryland is so narrow at its western end: at Hancock the state is less than 2 miles wide between the Mason–Dixon Line and the Potomac. The tangent line and the arc gave Delaware its unusual shape and the small "Wedge" of land that was disputed between Delaware and Pennsylvania until 1921. The line is also the southern boundary of the Appalachian ridges' Pennsylvania section, and it crosses the Susquehanna, the Potomac tributaries and the Allegheny Front on its way west. Culturally it still marks the northern edge of the Census South: Maryland, Delaware and West Virginia count as Southern, Pennsylvania as Northeastern.
Related maps
- Ohio River — the line's western extension in popular usage.
- Appalachian Mountains · US coastlines.
- Pennsylvania · Maryland · Delaware · Mid-Atlantic states · All geography maps.