One interesting pattern is that WV is not part of the South, but shares more with PA and OH.
I assume that the size of the circles indicates the strength of the relationship. So we are looking at something similar to maps of religion affiliation, where a "dominant" group is only a weak pluralistic. If the Appalachian and Lower Midwest group and Upland South groups were combined, there might be a stronger showing further west.
We tend to forget how difficult it was to migrate by wagon, horseback, and foot. It is hard to take a wagon over a mountain.
The Appalachian and Lower Midwest group came down the Valley of Virginia and through the Cumberland Gap into Kentucky and then on into Indiana and Illinois, and then Missouri.
Virginia kept West Virginia when Kentucky was detached in hopes of developing its own route to the west. New York had the advantage of an easier path for its Erie Canal. Pennsylvania eventually developed its combined canal and rail system, but by the time it was completed it was possible to build a railroad. Virginia did not have a significant port, and the national government was not inclined to develop its own route up the Potomac.
At the time of its secession, West Virginia was dominated by the counties along the Ohio and the north. In 1880, the most populous counties were Ohio River: Marshall, Mason, Ohio, and Wood; North: Harrison and Preston; and south central: Kanawha.
By the time the coal industry developed it was possible to migrate by train, and the demand for workers was more than could be accommodated by farmers from the immediate area. At the time of separation, West Virginia had about 35% of the population of Virginia. This peaked in 1930 and 1940 at about 70%, and like Maine and Massachusetts, there would be at least a fantasy of the child surpassing the parent in population. West Virginia is now down to 23%, about the same as 1840.
It is interesting that Wisconsin and Iowa are largely blank. Perhaps the German population was more diverse, than the Scandinavian population??? In Texas at least, German migration tended to be part of specific migration schemes, so that for example, counties in the Hill Country tend to have distinct religious beliefs.
A question about the Finns in UP and the Iron Range, are they primarily Suomi (as opposed to Swedish speakers)? If someone migrated from Aland or the west coast, would they just move to Minneapolis, Rockford, New York City, or Worcester and become Swedish?