Global Heat Map Showing Running and Biking Activity
Strava, an online activity tracking community, has created a global heat map of running and biking trails, utilizing a dataset of 77 million rides and 19 million runs. Zoomed out, the Google Maps overlay offers insight into where people are doing the most running and biking (or at least where people are logging those activities the most through Strava). Drill down and you can the most popular paths in a given area.
via FlowingData