The map is slightly deceptive when it comes to Virginia; here the cities are independent of the counties that often completely surround them, and so "city or co

The map is slightly deceptive when it comes to Virginia; here the cities are independent of the counties that often completely surround them, and so "city or county" is an equivalent-level government. So you see all the darkest-red dots running up the western part of Virginia? If the population in those cities were shared with the surrounding county and the density recalculated, you'd get a lot more of the middle-reds you see in western NC and SC. So the "Atlanta-Greenville-Charlotte-RTP" band that you see really continues all the way up to DC (where it becomes even denser and turns in to the Northeast Corridor Metroplex).