They generally just use the OS location and compass APIs but some apps definitely do go above and beyond by using the movement sensors. Pretty sure that Google Maps uses it.
OS APIs for location on Android and iOS both have support for supplementing GPS usage with their network-based location services. They send data like nearby cell towers to Apple / Google services and get back coarse location information.
Android supports implementing other supplementary location services but they need to be bundled with the OS and added to a whitelist so there isn't really much of an ecosystem of those because they would need to be done partnered with device vendors in their fork of the OS.
Mozilla made a service like this too, presumably for FirefoxOS.
It's technically possible to implement an entirely local supplementary location service with a cell tower database. Regional database for that in a good format isn't huge but it's not what Apple/Google/Mozilla did.
It's technically possible to implement an entirely local supplementary location service with a cell tower database. Regional database for that in a good format isn't huge but it's not what Apple/Google/Mozilla did.
