You already know that a smartphone can follow your location wherever you go but you may not be aware of that Apple not only tracks but saves your location virtually every minute.
Chances are, you've given Apple permission.
You'll find the information deep in your settings. Open settings and privacy, then location services. Down at the bottom of that screen you'll see an option for system services, and near the bottom of that screen is "Frequent Locations".
When you select that option you can see the history Apple has and keeps on your location. If you traveled to New York City for a meeting, you'll see where you stayed and where you might have eaten dinner. Once you select one of the cities Apple has saved your location information, you'll see exactly where it is on a map along with how many times you've been there and the time you arrived and left that address.
Apple states that it's harmless and allowing the iPhone to learn places you frequently visit provides useful location-related information in Maps, Calendar and more.
If this is all too creepy for you, there is an option to turn off the setting. You can also leave it on but clear out the history.
I've tried it both ways and did not notice any loss of functionality and if there is a lag in connecting to maps etc, it is negligible.
Android fans are not immune from being tracked by a parent company. Google also tracks and maps frequent locations for the same reason.