TiPb Answers: Why Does My iPhone Think it's in a Different State?

TiPb loves answering your questions, but we also love sharing our answers with the community in hopes that more people will benefit, and even better answers will present themselves (hey, that’s why we have them forums!). Today’s question comes from Stupendoussteve on Twitter:

ever heard of iPhone finding you at a previous address, states away, where you've never even taken the phone (post restore)?

We have! And TiPb answers after the break!

The iPhone uses Location Services to determine where it is. Location Services uses three (3) distinct technologies, and different iPhones (and iPod touches) support different levels.

The most precise, supported only by the iPhone 3G, is aGPS. aGPS uses cell tower-based GPS crunching to give you a fairly tight indication of your current position.

Next is cell tower triangulation, supported by iPhone 3G and the original iPhone 2G. Google mapped all cell towers in the US (and other countries), recorded their GPS locations, and then tries to determine where you are if it doesn't have -- or can't get to -- an aGPS signal proper.

The last -- and the one causing your problem -- is WiFi router mapping. Skyhook got into a bunch of vans, drove around the US (and other countries), detected WiFi routers in homes and businesses, and recorded their unique IDs along with their GPS locations.

For iPod touches, and for iPhones that aren't getting good aGPS locks, Location Services uses WiFi mapping to find out where you are. The problem you're encountering is likely that Skyhook recorded the location of your WiFi router when you lived in another state, and now when your iPhone is finding it, it still thinks you're at that old address, across town, or across the country.

Skyhook may eventually drive around and re-map your WiFi router, or you can go to SkyhookWireless.com and manually re-locate your WiFi in their system -- though in our experience it can take a long time for them to update either way.

Rene Ritchie

Editor-in-Chief of iMore, co-host of Iterate, Debug, Review, Vector, and MacBreak Weekly podcasts. Cook, grappler, photon wrangler. Follow him on Twitter and Google+.

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Reader comments

TiPb Answers: Why Does My iPhone Think it's in a Different State?

4 Comments

In reality, cell triangulation is the third and least precise method, while SkyHook WiFi positioning is the "middle" method.

Also more info on Skyhook:
If you did indeed move your router across country you can fix your wifi location via this page: http://www.skyhookwireless.com/howitworks/submit_ap.php
(You can also game the system from this page if you prefer to play the griefer.)
But another point of interest is that it does not have to be YOUR wifi that moves, or even one you are connected to. Nor does it have to be connectible (by you).
Every packet from the wifi router carries its mac address, and the mac address is used to look it up in the Skyhook database.
Your iphone can see a lot more wifi routers than it will show you. (Download WifiTrak from the app store if you don't believe this).
The phone will get the mac address of every router it can see and it only takes one rogue router to slow down and make imprecise any position hints Skyhook supplies.
I live in a area that has a lot of Military Officers who live off base and have wifi. They never reset it when they move. They move fairly frequently. There always seems to be a Rogue Router in my neighborhood throwing off my location in one direction or the other, often by dozens of miles, which always made my GPS pindrop sloooow.
I went to the above page and registered MY router, and that seems to help.
Most info I have seen on this subject (including some on the infinion site, the suppliers of the AGPS chipset) suggests that the wifi and tower locations are fed to the AGPS chip as the starting location, making satellite acquisition faster. (The chipset knows which birds are overhead and the frequency to listen on given this hint).
The only time you get a blue-dot is when there is a satellite fix, not a tower or wifi fix.
And skyhook does not work at all if you have no network connection, (No wifi, no 3G no edge).
This means your AGPS chip is on its own, and it can take it quite a while to work out its true position without these hints, but it will eventually.