What did the Mason-Dixon line separate in 1820?

The Mason-Dixon line is the dividing line between the states of Pennsylvania, Maryland D.C. and Delaware.

Surveyed and laid over 150 years ago by Charles Mason and Jeremiah Dixon.

Mason was an astronomer employed by The Royal Society in Greenwich, England.

Dixon was a surveyor from Durham, England.

Mason and Dixon set out to settle what had been a bloody land dispute between two families, the Calverts of Maryland and Penns of Pennsylvania, that had been waged for over 80 years. In 1763 Mason and Dixon were hired to settle the land dispute and set down stone markers to delineate the property lines.

Using precision astronomy instruments of the day (they used the stars to determine the border) and large limestone blocks that were 3.5 ft to 5 ft long and weighing around 300-600 pounds, as markers, they took 5 years to lay the boundary. When modern surveyors with the Mason-Dixon Line Preservation Partnership (MDLPP), used a GPS to check the boundary they found Mason and Dixon is amazingly accurate and the greatest variation is about 800ft. Much of the border wound it's way through 233 miles of rugged wilderness and difficult terrain.

A library of documents, papers and articles can be found in the library section of the MDLPP website at http://wiki.answers.com/"http://www.mdlpp.org/"

The actual story of the dispute and how the border was laid can be found here http://geography.about.com/od/politicalgeography/a/masondixon.htm

This site has some excellent photos of some of the markers (the limestone blocks were quarried and shipped from England, by the way) that still stand.

And this link shows the original Mason-Dixon line