Douglas County to the far south may be considered a part of the metropolitan area as may Boulder County to the northwest. The total population is over two million.
There is some cooperation in the metropolitan area in mass transit, but generally each county and its various towns are self-governing. The character of the various parts of the metropolitan area vary widely with the most prosperous portions being Douglas and Boulder County, with Adams county being the most industrialized of the suburbs.
The entire metropolitan area sits in a valley, the Denver Basin, and suffers from air pollution known colloquially as the brown cloud, building up if the air is stagnant as it often is in the winter.