Ever since I saw Nikita Barsukov map running traces in a handful of European cities, I wondered what the paths looked like for others. A lot of people make their workouts public on a variety of services, so there's definitely accessible data. I use RunKeeper for cycling. I sampled from there.

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.

Update: I should point out that these maps were experimental and certainly don't show running coverage for all the cities. For example, if you look at the New York map, you'll notice that there are few running routes in Central Park, which doesn't make much sense. This has to do with how I fetched data and how RunKeeper encodes it. 

San Francisco makes sense -- people run where it's flat.

Pretty cool, and I keep incorrectly labeling things as Infographic when it's really pure Data Visualization.

These days I've seen both terms applied.