How do services like Google Latitude, through my browser, obviously through my Internet connection (Ethernet not Wi-Fi), obtain my location perfectly with only my current public IP address? By asking my ISP?
Answer
Google Latitude uses a proprietary Google service that operates on the exact same principal as the more popular Skyhook Wireless system. The software takes readings from your wifi adapter, and compares these to a database of known wireless networks and their locations, allowing for the triangulation of your position based on signal strengths. This allows the service to determine an accurate location without GPS.
The database of WiFi networks is quite extensive and comes from multiple sources. First, they likely import from public databases like WiGLE. Second, whenever a laptop running the service sees a new network, it's reported to the service. When multiple computers report a new network, its position can be triangulated based on the position of the known computers. It is fairly simple to keep a database of all wireless networks because all wireless networks (even those with the same ESSID) have a unique interface MAC address assigned by the manufacturer.
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