flok writes "There are a couple of commercial products which can tell you where you are by the MAC addresses of access points in your neighbourhood. E.g. the iphone uses a system like this. There's now an open offering for this: OpenWLANMap. With this website, you can enter your access point mac address with your GPS location and then others can use that to navigate. There is also an app for your mobile which automatically enters this data, and you can upload data from e.g. Airomap and other wardriving applications."