By population, the two largest counties in the Commonwealth of Pennsylvania are Philadelphia County in the east and Allegheny County in the west.
These two urbanized counties are in roughly the same population range. There are about a million and a half people in Philadelphia County, and Allegheny County is not far behind with about a million and a quarter.
In Philadelphia County, the larger of the two, there is one self-governing municipality: the city of Philadelphia, which is coextensive with Philadelphia County.
In Allegheny County, there are 130 self-governing municipalities. The city of Pittsburgh is the largest, but even Pittsburgh makes up less than a quarter of the population of Allegheny County. One of those other self-governing municipalities is a medium-sized townhouse development, Pennsbury Village, that formed a borough of its own after residents had a dispute with the township they lived in. The villagers, having taken up their torches and pitchforks, issued a Declaration of Secession explaining “that we can govern our affairs more effectively and equitable [sic] than a distant and disinterested authority.” (The authority, Robinson Township, had its municipal building 3¼ miles from Pennsbury Village—pretty much equivalent to the Atlantic Ocean between them.) That is the fourth-smallest municipality in Allegheny County. The smallest is Haysville, consisting of 36 houses with a total of 81 people in them, where presumably everyone, children and pets included, has to take shifts running the borough government.
Everything that is different about Pittsburgh from its rival to the east, both for better and for worse, can be explained by these two numbers: 130 and 1.