Wi-Fi and your location

[yohaniv]

I am curious, how precise can ipad locate you just with Wi-Fi. And how it works anyway. I know there is a base of known Wi-Fi hot spots, and then there are IP vendors with known locations, but beyond that ...

When I first took that device to my home, it positioned me about 150 meters away, from my current position (using maps), but when I upgraded to 5.0 beta it pins me up just about 40 meters...

Your experience?

 

[CyBeRino]

I am curious, how precise can ipad locate you just with Wi-Fi. And how it works anyway. I know there is a base of known Wi-Fi hot spots, and then there are IP vendors with known locations, but beyond that ...

When I first took that device to my home, it positioned me about 150 meters away, from my current position (using maps), but when I upgraded to 5.0 beta it pins me up just about 40 meters...

Your experience?

It takes identifying features of wireless base stations (notably the BSSID and probably the ESSID, also known as the network name) and ties them to a location using GPS. This is done with devices that know where they are and what networks they can see there: "I am at location Foo and I can see networks X, Y and Z". This information is then put in a big database.

Devices that can see the networks but don't know where they are can then approximate their location by asking for the reverse information: "given I can see networks X, Y and Z, where am I?".

This works most of the time to a "good enough" accuracy. But it fails in two situations (besides the obvious one where you're out of reach of any wifi base stations): you can see only one and it's moved from its original position or, related to that, you're on a train, plane or other moving vehicle with wifi.

 

[Ashka]

Make that fails in three situations

Share 3G data on a Mac via WiFi with your iPad and it puts you back in the last place you used a real WiFi connection.. At the moment my location is 546 kms (339 miles) out. No other WiFi option at the moment and it doesn't put you back to the last 3G location if used on the iPad..