Every year the Internal Revenue Service releases data on the migration of families to and from every county in the United States. The statistics are voluminous and costly. (The IRS charges $200 per year for nationwide data.) Even if you get the database, it's difficult to get a good mental picture of the migration pattern for a given county. Fortunately, Forbes Magazine has developed a slick online map which easily visualizes the flow of people in and out of a specific area during 2008 (the latest year available).
Here's how it works: zoom in and click on a county. A set of lines appears connecting that county with every other country where at least 10 people have moved in or out. Black lines represent net inward migration, red lines net outward migration. Click on the destination county to see the raw numbers.
Sacramento County, for example, shows much movement to and from the urban centers of the East and West Coasts. A few 2008 highlights;
Boston (Sufflok County, Mass.) -- 40 people inbound to and 24 people outbound from Sacramento County.
Manhattan (New York County, N.Y.) -- 74 inbound, 62 outbound.
Washington, D.C. -- 56 inbound, 40 outbound.
Seattle (Kings County, Wash.) -- 495 inbound, 299 outbound.
San Francisco County -- 808 inbound, 796 outbound.
Los Angeles County -- 1,559 inbound, 1,854 outbound.