[Quixote]

Philadelphia is too large, old, established, economically self-sufficient, and culturally distinct to ever “belong” to NYC even in a connotative sense, much less formally.

Chicago and Milwaukee share a similar dynamic, but Philly is much more able to hold its own against NYC, being that it’s the primary city in a much larger and quite frankly more important state (the PA portion of Philly CSA accounts for 36% of the state population). I also think having DC-Baltimore to the south helps Philly’s case for independence as a sort of “crossroads” of the heart of the NE corridor (apologies to Boston).

Tilting the north-south axis, 6.27 million Delaware Valley residents (Philly CSA) live at or below Philadelphia city/County’s northernmost boundary; only Bucks and Burlington Counties are excluded. But most of Burlington County lives below this threshold, so the number is really closer to around 6.6 million. South Philly and the stadia complex, airport, and Wilmington give Philadelphia city a southern tilt; West Philly, UPenn, Main Line suburbs, and Reading a western tilt; and South Jersey with its 1.875 million residents (two-thirds living in Camden, Burlington, and Gloucester) provides balance to the east. Bucks County plus the 50/50 counties of Mercer and Hunterdon combined have a smaller population than Camden, Burlington, and Gloucester combined.

All of this is to say that Philly is easily its own entity. Mercer County is the only real overlap with NYC. Otherwise, sparse Hunterdon provides a good-sized buffer, and demarcating North and South Jersey is pretty easy. There aren’t any major population centers in South Jersey that border Ocean and Monmouth Counties; most of populated South Jersey lies directly across the Delaware River from Philly.