Infographic: To Map Cross-Country Migration, Just Follow the Money

Mapping migration patterns across America is harder than you think. Using airplane flight-data doesn't capture people's everyday travels. And you can't track everyone's everyday car movements (legally).

So Christian Thiemann and Daniel Grady of Northwestern University found an alternative: the flow of dollar bills. Specifically, they used data culled from Where's George, a website you can enter in the serial number of a dollar bill you have. If that bill is already in the database, the site tells you where other people were located when they possessed the same bill. Check it out:

While the study's aim was to track migration patterns in the U.S., the researchers zeroed in on large-scale communities in the U.S. In other words: Where are the social boundaries between the Northeast and the Mid-Atlantic? Or the Southwest and Pacific Coast?

The results actually square pretty well with what Pete Warden was able to create by analyzing Facebook networks. (Facebook forced Warden to delete the data, even though it was all public.)

Apparently, the Where's George data has had other applications as well. As Visual Complexity notes, epidemiologists are using it model the spread of the flu. Are you listening, Facebook?