As much as I love Philly, I'd have to say it's probably not the most populous city in the UCAS. Seattle is probably #1, but Philly's definitely in the top 5, if not top #2.
Seattle is at, what, 3 million in 2072? That's five times the population of today, but understandable since much of the Northwest flocked there and then it became a boomtown.
The top five of today are, in order, NYC, Los Angeles, Chicago, Houston, and Philly.
New York went through the quake and lost Manhattan. LA was California Free State but now makes up about half of the PPC population. Chicago flatlined. Houston's in the CAS. Philly's the only one that hasn't had a disaster.
(The next five, again in order, are Pheonix Arizona, San Antonio, San Deigo, Dallas, and San Jose. Indianapolis is the third largest USA city still in the UCAS.)
(Oh, Toronto crops up above Indy once you add in Canadian cities.)
I boosted Philly from the current 1.5 million to around 6 million, drawing on refugees from New York and, later, from Boston, but, Rotten Apple didn't exist at the time and that could change things on my end.
So, the top four in 2072, but NOT in order, are New York City (Which, minus Manhattan, you almost expect them to fracture into four normal-sized cities, but that goes against the Metroplex idea), Philly, Seattle, and Toronto. Indy may well be #5.
...
Not that this exactly means anything, but hey.
