The Third Avenue Bridge: one way to get from Manhattan to the Bronx (although we assumed most of these bikers made a round trip).

Jim Henderson

The Third Avenue Bridge: one way to get from Manhattan to the Bronx (although we assumed most of these bikers made a round trip).

A surge of Bronx pride led me to tweet in triumphant fashion yesterday about the news from the Census Bureau that from July 2014 to July 2015 the city’s northernmost, only mainland and all around best borough posted the fastest population growth of any county in the state.

One savvy reader wondered: “Anything to do with the mass exodus from East Harlem + Washington Heights due to rising rents + evictions?”

Here’s my long and wonky answer to that simple question:

Population change is a dynamic thing, reflecting not just what the incumbent population does (i.e. have babies or die) but also how many people move from or to a foreign country or another part of the United States, be it Yonkers or Ypsilanti. That net movement of people in and out of a county can also reflect multiple storylines – people coming from place A for one reason, and heading to place B for another.

It’s not possible just from looking at the latest numbers to say that there was an exodus or, if it existed, what impact it had last year. What we can say, based on the numbers the Census Bureau provided for 2014-2015, is that while the movement of people from Manhattan to the Bronx may have been part of the story, it wasn’t the story. The Bronx lost 15,000 more people via domestic migration last year than it gained. This was offset by solid in-migration from overseas and a healthy natural increase of births minus deaths.

(The Census Bureau notes that the numbers for the components don’t match the overall population change much because of a residual that “represents the change in population that cannot be attributed to any specific demographic component.”)

But wait, there’s more: If you look a little further back and over a longer period of time, you can say more about how the Bronx’s population has interacted with its fellow boroughs’.

Thanks to a super-cool Census Bureau tool called “the Flow Mapper” you can see where county residents came from or went to during, say, the 2009-2013 period. And over that date range, it’s clear that there was a very significant in-migration to the Bronx from Manhattan and, to a lesser extent, from the other boroughs:

A final note: As wonderful as the Flow Mapper is, it can’t tell us why people are moving. One might fairly surmise those moves to the Bronx were influenced by the housing market. But one can’t eliminate the possibility that something else shaped those decisions to relocate: Perhaps folks yearned for a home that is more convenient to the Arthur Avenue Retail Market or, heck, just wanted to live closer to me.

The key takeaway is, whatever mix of personal reasons shaped these movements, the Bronx is growing and public policy has to respond to that.