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?