I live not far from the 280 highway on Potrero Hill. The closest park is 3 blocks away, and the nice streets with trees, flowers and commerces are one block away.
But all we get in my street is the highway, and a small neglected space where people walk their dogs without pickup behind. Well, until now. Some neighbors apparently decided to reclaim this space from poop machines and cars. I found a note in my building asking for help in the adventure. There is even a blog.
I'm not a garden-type of guy, so maybe I missed it, but I've never seen such a thing in France, and I find it awesome. I really like the fact that people here are owning their neighborhood, helping cleaning and planting it among other things.
In France, as far as I remember you have your garden and you take care of it (or you pay some company to do it for large properties), or it's a public space and you don't touch it, the city manages that using your taxes.
That way I learned about Guerilla Gardening apparently going as far as taking action during the night. Well, no such thing in the preseng case, the dedicated neighbor that took the lead of this "subversive" operation contacted cityhall about the issue and got some kind of "permission".