An iPhone Knows Your Significant Locations

Keep in mind that iPhones use a particular method to track the smartphone's location known as 'significant locations'. This function can be accessed under Privacy and Security in Location Services.

. . . after the list of app specific settings in Location Services you'll find 'System Services' [note the color coded flag of a gray arrow showing that an app has tracked the phone's location in the last 24 hours and a purple arrow when an app has tracked the location very recently.]

Scroll down and you'll see the 'Significant Locations' option.

Apple states that the location data is encrypted, and that it cannot access it itself - (unless it is subpoenaed to produce it??).

The Apple policy linked to under 'Significant Locations' states that it uses the data to track the movements of groups of people and automobile traffic. Note that Apple also reserves the ability to estimate your location based on your IP address.