When you open your favorite map app and ask, "what is my current location?", a blue dot appears on the screen almost instantly. You might assume this is purely the work of GPS satellites orbiting the Earth. While GPS plays a role, the real hero of urban navigation is actually Wi-Fi tracking.
The Limits of GPS
Global Positioning System (GPS) is incredibly accurate, but it has one major flaw: it requires a direct line of sight to the sky. If you are inside a shopping mall, an underground subway station, or surrounded by skyscrapers, the weak satellite signals cannot reach your phone. If your phone only relied on GPS to find your my location right now, you would constantly lose your signal indoors.
How Wi-Fi Positioning System (WPS) Works
To solve the indoor problem, tech companies developed the Wi-Fi Positioning System. Even if you are not connected to a Wi-Fi network, your phone is constantly scanning for the names (SSIDs) and MAC addresses of nearby routers.
Companies like Google and Apple have spent years mapping the location of almost every Wi-Fi router in the world (often by driving camera cars down the street). When you ask your phone "what is my current location", it looks at the 3 or 4 Wi-Fi routers it can see around you, checks their known locations in a database, and triangulates your exact position.
Working Together
Modern smartphones use "High Accuracy Mode" which blends both technologies seamlessly. It uses Wi-Fi to get a fast initial fix and keep track of you indoors, and uses GPS to track you accurately when you are driving down a clear highway.