There are many apps that use the iOS location services. Apps such as Maps, Camera, Weather, App Store, Safari or even Dropbox. If you’re using at least one such app for location specific info, you have Location Services enabled on your iOS.
When Location Services is turned on, by default Frequent Locations is enabled. Frequent Locations is an iOS system services that record “places that you frequently visit in order to provide useful location-related information”.
To locate this settings, go to Privacy > Location Services on Settings app. Scroll all the way to the bottom and locate System Services > Frequent Locations.
For each frequent location in the History list, tap on it to display a map and detail timing of when you visited the place. You can clear this history if you choose by tapping on “Clear History”.
These Frequent Locations info is cached in your iOS devices. If you have “Improve Maps” settings switch on, these location info will also be accessible by Maps and other Apple apps such as Reminders. This is to allow Apple apps to give you more useful location-based info. It is anyone’s guess if Apple is storing these info on their server. If you’re not comfortable with these info available anywhere, just turn off the switches for “Frequent Locations” and “Improve Maps”.