Thursday, April 21, 2011

Apple Location Services

My iPod Touch doesn’t have a GPS receiver, so the only way it knows my location is by looking up the detected WiFi networks in a database. The first and most famous such database is Skyhook, and Apple used to use them, but last year they parted ways, and Apple switched to an in-house database.

How do these databases know how to map WiFi networks to geographic location? Well, you can imagine driving a vehicle all over the place, like Google StreetView. In fact, the Googlemobile did detect wireless networks, and got in trouble for collecting a bit more data than was necessary. But I’m sure that kind of survey is one source of data.

The Apple and Skyhook databases seem better than that, though—they’re more up-to-date and complete than I could expect from vehicular surveys.

I think they answers is that the mobile devices automatically report updates back to the servers. If you determine your location based on 3 networks that have been around a while, but now there’s also a 4th network, that new network gets added to the database in the same area. Skyhook calls this a “self-healing network.”

Better yet, if you have an iPhone with a GPS (or geolocation based on cell towers), it could tell the mothership about new WiFi networks, using the GPS as the means of location.

I live on a rural property, where my home network is the only WiFi network around. It’s surely never been surveyed by vehicle. As a result, my home network is not in Apple’s database, and my iPod Touch does not know its location when I’m at home. Unlike Skyhook, Apple doesn’t provide a web interface to add a new network to the database.

I’ve often wondered… if someone with an iPhone came for a visit, would my network be added to the database?

Anyway: The recent discovery of a location history stored in iPhones has been all over the news. I wonder if this history is somehow related to updating the Apple Location Services database?

Sen. Al Franken’s office has prepared a list of questions for Apple about this data, and they’re remarkably good questions. Better than I’ve come to expect from politicians: they hit the key issues and are technically sound. I look forward to Apple’s response.

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