Using aggregated data recorded on RunKeeper (so many running apps!), someone created maps that show the most popular running areas in several major cities. From Flowing Data:
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. [...] The maps below are what I got, mostly for American cities, but there are a few European cities in there too (alphabetical order). If there's one quick (and expected) takeaway, it's that people like to run by the water and in parks, probably to get away from cars and the scenery. In the smaller inland cities, there seem to be a few high-traffic roads with less running elsewhere.Thanks to Steve for sharing!