A feature called Significant Locations [zdnet.com] collects a detailed history of places you visit on a regular basis. The feature can be disabled via Settings > Privacy > Location Services > System Services > Significant Locations. The feature can be disabled, and history of data collected can be deleted. Most iPhone users are unaware that their phone records their current location and calculates which locations are significant. It's 2018, so why hasn't Apple made people more aware of this potential violation of their privacy? Apple claims that Significant Locations are encrypted and cannot be read by anyone except the phone owner, and if you believe this I have a bridge for sale you might like to buy.