How GPS Works on the iPhone

GPS makes location services work, but it comes with privacy concerns

The iPhone's GPS and location technology powers many useful apps.
Apple

Your iPhone includes a GPS chip just like the one found in stand-alone GPS devices. The iPhone uses the GPS chip in conjunction with cell phone towers and Wi-Fi networks—in a process termed "assisted GPS"—to quickly calculate the phone's position. You don't need to set up the GPS chip, but you can turn it off or enable it selectively on the iPhone.

GPS Chip

GPS is short for the Global Positioning System, which is a satellite constellation and support infrastructure put in place and maintained by the U.S. Department of Defense.

GPS finds a position by trilateration of at least three of a possible 31 satellite signals. Other countries are working on their own systems, but the U.S. system is the only one in wide use around the world. The only other system that is close in capability is Russia's GLOSNASS satellite system. The iPhone is capable of accessing both the GPS and the GLOSNASS systems.

One weakness of GPS is that its signal has trouble penetrating buildings, deep woods and canyons, including urban skyscraper canyons, which is where cell towers and Wi-Fi signals give the iPhone an advantage over stand-alone GPS units.

Managing GPS Information

Although an active GPS connection is vital for navigation and mapping apps, among many others, there are privacy concerns related to its use. For this reason, the iPhone contains several areas where you can control how and if the GPS capability is used on the phone.

Controlling GPS on the iPhone

You can turn off all location technology on the iPhone—which Apple does not recommended—by going to Settings > Privacy and toggling off Location Services.

Rather than doing that, take a look at the long list of apps on the Location Services screen below "Share My Location." You can set each one to Never, While Using or Always. The point is, you take control of which apps use your location data and how.

Accessing the App List

Tap the Settings icon and scroll down to the app list.

There you can tap on each app icon displayed to see how it interacts with GPS (where applicable) and your phone. You may toggle on or off various settings, depending on the app, including Location, Notifications, Use Cellular Data and access to your Calendar or Contacts and more.

GPS Complementary Technologies

The iPhone has several complementary technologies on board that work in conjunction with the GPS chip to master the phone's location.

  • Accelerometer and Gyroscope: The iPhone has an amazingly small 6-axis gyroscope and accelerometer combination chip on board. The gyroscope tells how your phone is oriented at all times. The accelerometer detects and records motions big and small as inputs the phone can use.
  • Wi-Fi Tracking: When GPS doesn't work well, such as inside buildings or among tall buildings, Wi-Fi tracking can replace or supplement it. Wi-Fi tracking uses a database of Wi-Fi networks around the world to triangulate the phone's position based on multiple Wi-Fi signals.
  • Compass: Your iPhone has a digital compass as part of its motion-tracking chip. The compass is used to supplement other motion technologies and to orient any map that you happen to be using. The compass comes into play, for example, when you tap the Maps arrow to orient a map. The Compass may also be used on its own.
  • Barometer: You might think of a barometer, which measures air pressure, as primarily a weather-prediction device, but it's not used for that purpose on an iPhone. The barometer supplements the GPS chip for measuring elevation changes to create more accurate elevation and elevation-change readings.
  • M10 Motion Coprocessor: In the iPhone, Apple uses its own M10 motion coprocessor chip to continuously measure data from the accelerometer, compass, gyroscope, and barometer. This offloads work from the A10 Fusion chip for improved power efficiency.