Actually it is, we do use both network cells and other public beacons for navigation when GPS is unavailable. It’s just not available everywhere – you need a map available of cell locations and usually this mandates open datasets for companies to use. Navigation works underground in e.g. Helsinki metro as a personal anecdote. We don’t need strict triangulation underground as cells are already so small. The metro tunnel is filled with picocells in practice (smaller than 200m coverage area cross-section).

We also use the cell network to push rough satellite locations to cellphones, in A-GPS, or more generally A-GNSSb as the same functionality is available for other systems as well. This way the phone can pinpoint the required satellites much faster, which is the main reason you can get such quick and accurate readings from your phone after starting to check your location.

Edit: AFAIK location services also enrich the information with databases of publicly visible WiFi SSIDs, using their visibility as a beacon. Scanning WiFi hotspots typically consumes less power than getting a GPS signal that’s as accurate, and is also often more reliable in urban settings and higher latitudes where the satellites aren’t as visible (though the constellations have enough satellites nowadays that this issue isn’t nearly as bad as it used to be)

It certainly used to be available in the days before GPS were in all phones. I remember my blackberry having a huge range for my current location on Google Maps because it was using cell phone tower triangulation. So maybe it is still there if you turn off your GPS?

Your phone uses tons of shit to figure out where it is. Cell towers, known WiFi access points, GPS, GLONASS, some others I forget the name of.

One time we moved a state away and brought our router without changing the SSID. For like 2 weeks our phones would show us back at the old place whenever we were on the wifi