This app allows you to browse street level map of San Francisco when you are traveling. You don't need to have internet connection for this to work as the map is stored on your iPhone or iPod Touch. Ideal for saving roaming charges or having to find the local wifi to access the built-in map application.
You can pinch to zoom in and out of the map just like you can with the built-in map application.
There is also support for GPS on the iPhone and iPod Touch (via WiFi).
The source of the map is from Open Street Map, under Creative Commons Attribution-ShareAlike 2.0 licence.