What you want are local parks you can walk to, so you can go out for a walk in the park. I don't see much of that in San Francisco, there are some parks but they haven't put local parks in every neighborhood as you would need.

The cities I am used to have parks at most 100 meters away from any home and a pretty large park 200 meters away, then anyone can go out and enjoy the park. San Francisco on the other hand seems to require driving to the park, but there isn't enough parking for everyone to enjoy the park anyway so most people don't have reasonable access, not comparable at all, the parks are giant though but they don't do anything for local neighborhoods. New York is kinda bad at local parks as well, but much better than San Francisco.