FAQ: How Google Latitude locates you [Computerworld]

Intriguing but also kinda scary…

Google is using technology from Skyhook Wireless in the Latitude service. According to Nick Brachet, Skyhook's chief technology officer, the company's XPS hybrid-positioning system is "a software-only location solution that allows any mobile device with Wi-Fi, GPS or a cellular radio to determine its position with an accuracy of 10 to 20 meters. What sets XPS apart is that it uses land-based Wi-Fi access points, GPS satellites and cellular towers to determine location information."

In other words, Skyhook's software can use any of the three kinds of signals — Wi-Fi, 2G/3G/4G mobile or GPS satellite — that a device can pick up to work out its location. By leveraging these wireless capabilities, Skyhook's software can combine positioning data from satellites, carrier assistance servers and Wi-Fi base stations to significantly speed up positioning, or TTFF (time to first fix). TTFF for some devices can be up to a minute, but the addition of Skyhook's XPS can reduce TTFF to a few seconds.

FAQ: How Google Latitude locates you