Obviously the coasts have a lot more population centers, which affects the average distance. But sometime swing over to Google Maps and start zooming in on a s

Obviously the coasts have a lot more population centers, which affects the average distance. But sometime swing over to Google Maps and start zooming in on a state in the center of the country, but stay away from the larger cities. You'll find a lot of places with pretty regular grids of roads, just spaced out more than they would be in a city (about a mile apart is pretty common). And if you think about what that land is used for, you'll probably be able to work out why they're there :)