The path through the Bible Belt captures the cities of Raleigh, Columbia, Atlanta, Montgomery, and Jackson. Cities in general pack more people per square foot than outlying areas. I suggest the key to electoral preference is population density. Stay with me here. The density of human bodies in a contained space, per se, gives rise to social stress.
Social stress gives rise to social problems such as alcoholism, crime, and violence.
The presence of social problems precipitates an interest in government intervention to solve the problems. Actually, none of the blue areas correspond with the Ohio river except around Pittsburgh. They're not along the Ohio River, though. The blue pattern does look, vaguely, like it follows the ridge lines of the western Appalachians, so there may still be a link between geography and voting here. I'd have to pull up a terrain map to be sure.