A: Evanston, Illinois, United States

1/26/2006

On January 26, 2006 Dirk Brockmann, a theoretical physicist and computational epidemiologist at Northwestern University in Evanston, Illinois, L. Hufnagel, and T. Geisel published "The scaling laws of human travel," *Nature *439 (2006) 462-65.

Using statistical data from the American currency tracking website, Where's George?, the paper described statistical laws of human travel in the United States, and developed a mathematical model of the spread of infectious disease.

[By January 31, 2009, Where's George? tracked over 149 million bills totaling more than $810 million. (Wikipedia).]