From Foursquare’s Vimeo page:
Every day, millions of people check in on Foursquare. We took a year’s worth of check-ins in New York City and Tokyo and plotted them on a map. Each dot represents a single check-in, while the straight lines link sequential check-ins.
What you can see here represents the power of check-in data — on Foursquare, every city around the world pulses with activity around places every hour of every day.