How does Chrome know my geolocation?

Question

Chrome seems to be very accurate in detecting my location. How does it do it? Can you point me to the source code?

Answer 1

Geolocation can be calculated based on:

1. GPS (if available)
2. Available wi-fi networks and signal strengths
3. Available cell towers and signal strengths
4. IP Address lookup

See the W3C Geolocaton API and Google Gears API (which Chrome's/W3C Geolocation API is based on).

Chromium's geolocation source code can be viewed online.

Answer 2

Your location can be obtain using different services and hardware available on your device. The most common ones are: GPS, wifi information, cell towers. Alternatively there is also IP lookup, however this is not very accurate and does not involve anything special on your device.

In your case most likely information about your wifi network was used. There are huge databases which connect wifi networks to a location, created by cars with GPS & Wifi (e.g. Google Street View cars). The transmission from your computer to the server is done according to W3C Geolocation API Specs, which is part of HTML5.

Chrome Source for this? Here is a entry point to start off from. Or if you prefer the old fashioned file browser: http://src.chromium.org/svn/trunk/src/chrome/browser/geolocation/

Implementation files for localization via wifi:

• wifi_data_provider_mac.cc
• wifi_data_provider_linux.cc
• wifi_data_provider_win.cc