 Most of the Delaware–Pennsylvania boundary is an arc, and the Delaware–Maryland boundary does not run truly north–south because it was intended to bisect the Delmarva Peninsula rather than follow a meridian.The Maryland–Pennsylvania boundary is an east–west line with an approximate mean latitude of 39°43′20″ N (Datum WGS 84).In reality, the east-west Mason–Dixon line is not a true line in the geometric sense, but is instead a series of many adjoining line segments, following a path between latitude 39°43′15″ N and 39°43′23″ N.

The surveyors also extended the boundary line west of Maryland's western boundary, into territory that was still in dispute between Pennsylvania and Virginia, though this was contrary to their original charter.