Aha There It Is finds tennis courts in your area (as long as your area is the Bay Area, which is all they cover at the moment). What’s amazing is how the database came to be, which is is explained in this lengthy (and very nerdy) post. While I can’t pretend to really understand the process, basically the dude wrote a program to scan Google maps and find images that looked like tennis courts, which is totally awesome.
It also reminds me of a conversation I was having the other night about American cities that look like every other American city of its ilk (think Houston, Phoenix, Vegas, etc. … basically all the fastest growing places of the last ten years). Anyway, I was wondering whether you could look at the Google Maps aerial view of those cities and recognize them as similar to each other/locate more cities like them based on the footprint. Being that they all share some big similarities, especially around their preference for planned communities, I imagine there must be some patterns. Might be fun.