First take your handy dandy Android device and install Wigle Wifi Wardriving.
It uses the internal GPS and wifi to log access points, their security level and their GPS Position.
looks like this (yup i stole these)
List of access points
Also makes a cute map on your phone
once you have the APs you can export out the "run" from the data section. yes yes, the stolen photo says "settings" but if you install it today it will say "data" there now.
With the KML export you can import that directly into google earth and make all sorts of neat maps by toggling the data.
All Access Points
Open Access Points
WEP Encrypted Access Points