iOS System Services
(See the full article about Smartphone Location Tracking)
Details and recommendations on iOS system services that can transmit your location…
Cell Network Search
This collects data about cell towers within range of your iPhone and monitors reception in your area to determine patterns of cell usage, tower congestion, and so forth. It’s not a necessary function, so it's fine to disable it.
Compass calibration
The electronic compass shows you which direction you're facing when you use maps and navigation apps. The calibration service uses location data to make compass more accurate, so do NOT turn it off.
Diagnostics and Usage
Apple collects anonymous information about you and how you use your device. If you don't want to take part in Apple's quest to improve their devices, you can turn this feature off without any consequences.
Find my iPhone
If you lose an Apple device, this feature can help iCloud figure out where it is. You never know when you might need it, so it's probably better to leave this turned on. But you should know that anyone can use the iCloud website and Find my iPhone feature to locate, wipe, or lock your iPhone if they know your password. To prevent that, use a strong password for your Apple ID/iCloud account and enable two-factor authentication.
Frequent Locations
This logs locations you visit most often to give you traffic predictions and other occasional notifications. If you use traffic updates and other info on the Today view of your Notification Center, keep this service turned on. If not, just disable it.
HomeKit
This is of use only to people who use smart home devices compatible with Apple's HomeKit technology. If you don't do that, turn this feature off.
Location-Based Alerts
These track when you enter or leave certain areas and send you notifications, such as “call your spouse when you are near the grocery store” or “go to the meeting when you arrive at your office.” If you don’t use this feature, you can turn if off to reduce unwanted location tracking.
Location-Based iAds
These track your movements for advertising purposes. App developers can use this data to display targeted ads when people use certain app. If you want to opt out of location-based ads, you should choose to limit ad tracking on your device.
Motion Calibration & Distance
This is mainly used by health and fitness tracking apps. If you don't use these type of apps, you can disable this feature.
Popular Near Me
Your iPhone anonymously sends locations of where you have purchased or used apps. Apple uses this data to offer you apps and other products and services popular in your region. If you value your privacy, you can turn this off.
Safari & Spotlight Suggestions
These are based on the location information that Safari and Spotlight send to Apple when you submit a search query to the apps. The data is used to provide you with precise information based on your geographical location. If you rarely use Spotlight, you can turn this service off.
Setting Time Zone Automatically
This helps keep your clock and calendar accurate so it's useful for frequent travelers. If you rarely leave your time zone, you can manually set it as needed in the device's time settings and disable this feature.
Share my Location
Unless you use certain Apple apps to share your location with friends and family quite often, this can be turned off. Note that this switch doesn’t disable location sharing option for all applications; you’ll still be able to share your location in Google Hangouts and other apps.
Status Bar Icon
This is hidden in the very end of the settings list, and forces an icon to appear in the Status Bar every time any of above mentioned services tracks your location. Turn this option on and it will remind you to check the settings next time you see unexpected activity of location services.
WiFi Networking
This works just like Cell Network Search, sending data to Apple about WiFi networks located within range of your iPhone. On the one hand, it helps Apple make location services more accurate. On the other hand, it helps the company track you even when you turn GPS off. It's your call whether to leave this on or not.