Where do they come from? Where did they go?

Forbes has published a fascinating interactive map that shows domestic migration trends by county for the past several years. 

Poking around the data, a few things struck me:

• More people left San Francisco each of the last five years than arrived.  Since the Census Bureau figures (upper left) show an overall increase in population, that growth is fueled by international immigration.
• The largest number of people leaving San Francisco head for the nearby counties (San Mateo, Alameda, Contra Costa, and Marin).
• Santa Clara, Los Angeles and San Diego counties are the largest source of arrivals.
• The largest source of incoming folks from outside California seem to be from Cook County (Chicago, IL), Middlesex County (Cambridge, MA), and Maricopa County (Phoenix, AR).
• The most popular destinations outside the state were Multnomah County (Portland, OR), Travis County (Austin, TX) and Harris County (Houston, TX).
• Marin County gets most of its incoming folks from San Francisco followed by Alameda, Contra Costa, Los Angeles and Vallejo.
• Most of Marin's departures seem to go one county north to Sonoma.

Take a few minutes to play with it.  Suggestion:  click on "hide lines".  They make for a pretty graphic but get in the way when you're trying to see detail.  Plus, they give something of a false impression.  Just looking at the San Francisco graphic above you could easily conclude that we import more folks than we export.

Also, try clicking through the years.  For San Francisco, you can see that from 2005-2007 more people were heading to the Seattle area than were coming into the City.  By 2009 and 2009 that trend had completely reversed.