Tin Isles

The article you are reading has moved! It is now available at: http://blog.tinisles.com/2009/12/wifi-geolocation/

Playing around with Google Latitude I was VERY surprised to see Latitude work out my exact location. How are they doing this? I don't have a GPS in my netbook?

Turns out they use wifi location to do this. When Latitude determines your location it gathers up a list of all the nearby Wifi SSIDs / MAC addresses and sends this to Google. Google have a database of Wifi access point locations created by driving cars around. This database, in combination with the nearby Wifi details, is used to determine your location. Pretty amazing that this actually works! Skyhook wireless is the first company I heard about building a Wifi database.

Always curious to see this stuff in action I fired up Fiddler to see exactly what is being sent to determine my location.

Request:

POST /loc/json HTTP/1.1

{
  "access_token": "2:Fv--0aj9-Vr4_3ir:8uFyciMoILwtrXry", 
  "host": "lfkq9vbe9u4sg98ip8rfvf00l7atcn3d.ig.ig.gmodules.com", 
  "radio_type": "unknown", 
  "request_address": false, 
  "version": "1.1.0", 
  "wifi_towers": [
    {
      "mac_address": "00-0b-6b-81-7b-14", 
      "signal_strength": -72, 
      "ssid": "OA0509-0077-1-M"
    }, 
    {
      "mac_address": "00-0b-6b-81-7d-0d", 
      "signal_strength": -78, 
      "ssid": "OA0509-0096-1-1"
    }, 
    {
      "mac_address": "00-0b-6b-81-7d-0f", 
      "signal_strength": -85, 
      "ssid": "OA0509-0052-2-1"
    }, 
    {
      "mac_address": "00-0b-6b-81-7d-29", 
      "signal_strength": -80, 
      "ssid": "OA0509-0096-2-1"
    }, 
    {
      "mac_address": "00-0b-6b-81-7d-8a", 
      "signal_strength": -82, 
      "ssid": "OA0509-0101-1-1"
    }, 
    {
      "mac_address": "00-0b-6b-81-7e-bd", 
      "signal_strength": -79, 
      "ssid": "OA0509-0052-1-1"
    }, 
    {
      "mac_address": "00-22-3f-9b-f1-a4", 
      "signal_strength": -61, 
      "ssid": "2/107"
    }
  ]
}

Response:

{
  "location": {
    "accuracy": 165.0, 
    "latitude": -33.874097499999998, 
    "longitude": 151.20640280000001
  }
}

Want to add geolocation to your own web application? Check out the Google Gears Geolocation API, or the Firefox's geolocation object