Follow the Money: Human Mobility and Effective Communities

Ever wonder where your dollar bills travel after you plop them down for a cup of coffee? The Web site Where's George? allows you to do just that: Record your bill's serial number and then track its journeys as other people spend it across the country. But it's more than just a game. Because every time a dollar is spent in a new place, it means someone moved it there. Christian Thiemann and Daniel Grady of Northwestern University in Evanston, Illinois, have been using the Web site's data to study how people move within the United States.

Image credit: Christian Thiemann and Daniel Grady, Northwestern University