City Limits ExplainedThe biggest reason that Pittsburgh appears to be shrinking while other cities -- such as Houston, Phoenix and San Diego - are enjoying a population boom. is that its city boundaries remain virtually unchanged from horse and buggy days, while the Sun Belt cities are continuing to annex their suburbs. Houston went from 17 square miles in 1910 to 579 square miles in 2000. Phoenix now consumes more than 27 times the area reported in 1950. San Diego has more than tripled in size in the same time period. Pittsburgh, in contrast, hasn't expanded its city boundaries since annexing Allegheny City (now the North Side) in 1907.
Urban SprawlThe average city included in America's Top 10 is 340 square miles, more than six times the geographic size of Pittsburgh, at 56 square miles. Those mega-metropolises have spread out and swallowed their suburbs, broadening the city tax base to include as many people as they can. San Diego, the smallest of the 10 cities would swallow almost all of Allegheny County (which, incidentally, ranks at #30 among largest U.S. counties).
What This Means for PittsburghIf the Pittsburgh city limits were expanded to cover about the same area as any other Top 10 city, it would expand the city's population from roughly 330,000 to more than 1 million, making Pittsburgh the ninth largest city in the country. That's a pretty big change from #56.
The Pittsburgh Urbanized Area (UA), an area defined by the U.S. census as a city and its suburbs, is ranked #22 in the U.S. in population and #24 in the U.S. in terms of land area or sprawl (181.7 square miles). Then there is the Pittsburgh Metropolitan Statistical Area (an area defined by the Census Bureau as covering the counties of Allegheny, Armstrong, Beaver, Butler, Fayette, Washington, and Westmoreland). Using that demographic, Pittsburgh ranks #21 in terms of population amoung U.S. cities.