The more interesting question is, if we drew a straight line from the Pacific Coast to the Atlantic coast, which trace would yield the highest % of counties that voted for Clinton? My hunch is a diagonal from Southern California up to Maine's Southern coast, but I'm not 100% sure.
It depends on the map projection, but if I look at their map, I think that if you draw a line from Des Moines (Polk IA) to Cleveland (Cuyahoga OH) you can pass through a number of Clinton counties in eastern IA, IL, northern IN and OH. If I then project that to either coast it looks like it goes from near SF to NYC.
Edit: A great circle from SFO to JFK passes over the Clinton counties with Ames IA, Cedar Rapids IA, Chicago (4 counties in IL),
South Bend IN, Toledo OH, Cleveland OH, and State College PA.
Edit 2: With Google Earth the great circle described above passes over the following 24 Clinton counties:
CA (7) San Mateo, Alameda, Contra Costa, San Joaquin, Stanislaus, Alpine, Mono
CO (1) Routt
IA (2) Story, Linn
IL (4) DeKalb, Kane, DuPage, Cook
OH (2) Lucas, Cuyahoga
PA (2) Centre, Monroe
NJ (3) Union, Essex, Hudson
NY (3) Kings, Queens, Nassau (by extension to the coast)
I'm sure there are lines that are slightly better, but this had easy start/stop points.
