Since it is a special feature in Gears and many other products (Iphone,...) , I wonder how geolocalizing using Wifi exactly works.

I know that every access point distributes its beacon every few millisecs so they can be captured. But there has to be a vehicle driving around every major town of every country to capture all these beacons and map them to a specific location. I think this is very expensive..and can also lead to errors since you someone can have a new Wifi-router if he changes the ISP, the old is broken, etc..

Does anyone have more details how these beacons are retrieved and mapped ? And is there perhaps a open-beacon-database available for free that you can use for your own products ?

Here's some more info about how Gears does it, although it doesn't actually say how it knows the location of the WiFi access points:

<< The Gears Geolocation API can make use of network servers to obtain a position fix. The server determines the client's position using a set of data provided by the client. This data includes the client's IP address and information about any cell towers or WiFi nodes it can detect. >>

http://code.google.com/apis/gears/geolocation_network_protocol.html

I am guessing the Wifi Access points are located using SkyHook, which is used in the Google Maps app on iPhone and in the iPhone OS, and also on Eye-Fi camera SD slots, and in Mac OS X Snow Leopard.

http://www.skyhookwireless.com/ is the address.