Nathan Yau from FlowingData created beautiful maps by using publicly accessible exercise app data:
There are many exercise apps that allow you to keep track of your running, riding, and other activities. Record speed, time, elevation, and location from your phone, and millions of people do this, me included. However, when we look at activity logs, whether they be our own, from our friends, or from a public timeline, the activities only appear individually.
What about all together? Not only is it fun to see, but it can be useful to the data collectors to plan future workouts or even city planners who make sure citizens have proper bike lanes and running paths.