Several issues intertwine.
The border between Pennsylvania and its immediate neighbors, Maryland and W. Virginia was in dispute, about 4,000 sq. miles of territory were at stake. Current maps were inaccurate. So a more accurate survey was commissioned.
It made a great deal of difference to certain people, whether they were born on one side of the boundary or the other. Anyone born on the Pennsylvania side was born free; certain people born on the other side were born into slavery. I guess one could call that a political issue, since the country went to war over it a hundred years later.
What has gravity to do with the Mason-Dixon Line? Mason and Dixon were using a telescope to sight stars in order to determine latitudes and longitudes. To get an accurate fix on a star, the telescope had to be pointed at a known angle. To get the telescope pointed at a known angle, a plumb bob was used to determine the vertical as a reference point. One tends to assume that a plumb bob will always point straight down; not so. The lead weight was pulled off true vertical by massive bodies in the vicinity (e.g., mountain ranges), thus skewing the angle of the telescope and distorting the measurements, in places by as much as 900 feet. Mind you, Mason and Dixon could not have known this; they did exemplary work given the level of knowledge and technology available to them. Still, …
… suppose someone was born in that zone of error during the hundred years between the laying down of the markers and the Emancipation Proclamation; it could have made a freeman into a slave, or v.v, depending on which way the error ran.