Great concept! Voted for San Francisco to be the next city. You should have paths that go over hills (for a robust walk), and paths that go around hills (for a flatter stroll) too! :-)
Ha and you should name those routes "For the fit" and "For the sedentary"
KIDDING!
If you did this it would be meaningfully different from Google Maps for me, the other benefits that others have said so far don't really resonate with me personally
