New York City's next Williamsburg isn't located in Brooklyn or any of the other boroughs. You'll find the front line of Big Apple gentrification in Fishtown, a neighborhood of Philadelphia. In City Journal, Aaron M. Renn maps how NYC talent exports transform cities such as Philadelphia:
Certain regions don’t figure prominently in the net-migration rankings because inflow and outflow between them and New York are relatively balanced. Yet in some cases, very high numbers of people are moving between the two regions. For instance, the Boston metro area attracted only 2,800 net migrants from the New York area during the 2000s, but over the same period, a whopping 160,000 people either moved from Boston to New York or from New York to Boston. Similarly, 111,000 people moved between New York and the Bay Area in California, even though the former lost only 8,100 net migrants to the latter. High “circulation rates” like these are nothing to worry about. In the interconnected, talent-driven global economy, intense circulation between places like New York and San Francisco is key to the vibrancy of human-capital networks.
Emphasis added. I'm glad Aaron highlights Boston as I'm using Philadelphia to make the same point. Boston frets about brain drain to New York and San Francisco as if it were a bad thing. Here I am on record with Next City fêting Philly churn:
I like to look at net migration and gross migration, but prefer gross migration because I don’t really care which way the flow is balanced. The cities that you have a high level of exchange with are important for economic development. Looking at gross migration, New York is far and away the most important for Philadelphia. Number two is D.C., but it’s not even close. More than a quarter of the total migration is going on between New York and Philadelphia. Interestingly, the flow to D.C. when you’re looking at net migration is exceedingly negative. It’s one of the biggest brain drains for Philadelphia. Whereas New York, on net, is one of the biggest brain gains for Philadelphia.
Step 1, Philadelphia's best and brightest invade talent refinery New York. Step 2, these expatriates experience tremendous upward mobility. Step 3, Lena Dunham is the most boring person on the planet. Time to grow up and move somewhere else to raise kids, somewhere like Fishtown.
For Philadelphia, the relationship with Washington, D.C., is still at Step 1 or Step 2. Eventually, D.C. proper will make real estate refugees out of affluent whites. Whether or not that counts as gentrification, I'll let the critical theorists judge. They've cornered the market on all social justice issues.
Inter-urban connectivity isn't a firm thing. It's a migrant thing. Well done, Philadelphia.