iPhone 101: Location data and GPS

Recently, the Apple community has become interested in location data as gathered by iPhones. Specifically, The Guardian has reported that researcher and former Apple employee Pete Wardensome and data visualization scientist Alasdair Allan believe that your iPhone's travel history is backed up to a file on your Mac, eliciting questions and concerns about iOS location services.

With that in mind, TUAW offers this brief primer so that you can better understand what's going on under the hood of your iOS device when it comes to location matters.

What are location services and how do they work?

Location services allow certain apps to determine your iPhone's approximate location and make use of that information. This is done through a combination of cellular network triangulation, Wi-Fi triangulation and the Global Positioning System, or GPS.

Here's how it works. Your iPhone will first attempt to communicate with GPS satellites to determine its approximate location. This is a series of medium Earth orbit satellites deployed by the US Department of Defense several years ago. For a more in-depth explanation, look here.

When a solid GPS connection is unavailable (the iPhone is indoors, amid many tall trees outside, etc.), the iPhone tries Wi-Fi triangulation. As our own Auntie TUAW recently explained, this works because Wi-Fi hotspots rarely move. Apple has amassed a database of known hotspots and, when your iPhone is connected to one of those, can use them to determine an iPhone's approximate place on the Earth. Of course, this method is less accurate than GPS.

Finally, determining location via cellular towers works in a similar fashion. Nearly every cell tower is built in a known, constant location (except for COWs). These fixed positions allow your iPhone to determine an approximate location by triangulating its distance from the nearest towers. Cell towers are less accurate because there are fewer of them than there are Wi-Fi hot spots. Therefore, you're dealing with larger distances.

The first time an app tries to access location data, it asks for permission. A dialog box asks to use your current location. If you're OK with that, tap Allow. Otherwise, tapping Don't Allow prevents the app from accessing your location data until you turn it back on as described below.

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iPhone 101: Location data and GPS originally appeared on TUAW on Wed, 27 Apr 2011 07:00:00 EST. Please see our terms for use of feeds.




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