In addition to satellite navigation, mobile phones can also use crowdsourced cell sites and WiFi access points location data. Phones help each other by creating a centralized database of the locations of cell sites and WiFi access points. If satellite navigation is unavailable, then the phones can utilize this database to determine their positions.
Some documentations explain how a phone or device without GPS can determine its location. Flat-Earthers incorrectly use these documentations to “prove” GPS does not use satellites. In reality, there are various methods of determining location, not just GPS. These documentations explain location service using cell & WiFi crowdsourcing, which is different from GPS.
Phones continuously report their positions according to satellite navigation (GPS) and the list of cell sites and WiFi access points they see around them. These reports are sent to a central server owned by vendors like Google or Apple. Because there are many phones worldwide doing such data collection, the central server has a comprehensive database about the location of cell sites and WiFi access points.
Sometimes a device cannot use satellite navigation, like inside a building, for energy conservation or lacking the feature. If the device still has an Internet connection, it can ask the central server to determine its position. It can scan its surroundings for cell sites and WiFi access points and send it to the central server. The central server can then determine the device’s position and send it to the device.
Another technology that helps devices in determining their location is dead reckoning using the device’s motion sensor. From the last known position from satellite navigation and the device’s motion afterward, the device can calculate its current position even if it wanders into a location without a clear line of sight to the satellites.