In 2000, the metropolitan area of Pittsburgh was comprised of six counties and housed 2,358,695 people.
Only 334,563 of these lived in the "central city," the City of Pittsburgh.
The U.S. Bureau of the Census also has a spatial unit called the "urbanized area," that is more-or-less solidly built up, and contains Pittsburgh's suburbs as well as the central city. The UA had a population of 1,753,136 in 2000. Thus, Pittsburgh's suburbs contained 1,418,753 people in 2000, and were far bigger than the central city that they surrounded.
Beyond the suburbs is an area that is not solidly built up, yet is still considered to be part of the metropolitan area. This area lies in the "shadow" of what looks physically like a city. In the case of Pittsburgh, the shadow houses another 605,559 people.
