Percent of the population living in urbanized areas? (Or, perhaps, metropolitan areas instead?)
Close enough. It's actually percent of the population living in urban areas. Urbanized areas are urban areas with a population of at least 50,000, while urban areas are densely-populated settlements of at least 2,500 people. If this map was of urbanized areas, several states (such as Wyoming, Montana, and the Dakotas) would be several shades lighter.
Yeah, I meant to say "urban" rather than urbanized; also wasn't sure about how the different definitions might impact some of the shades, which I couldn't perfectly tell apart (esp. between 40% and 50%). I happened to remember that Maine was the most rural state in the Union, followed by Vermont, Mississippi, and West Virginia- four states with so little else in common demographically. So when they popped out as the lightest shades, I knew it had to be something like that.
