NavList:

For urban driving I wonder if cellular phone positioning, together with direction, inertial sensors, odometer and the assumption you were on a road would be enough. If not we are close to the point where a video stream matched to google street view would be computationally feasible. GNSS is only used in this situation as it there, free, and low computational cost.

I suspect dead reckoning (odometer and compass + known roads) would work fine  on rural road network too. Maybe assisted with computer read road signs. Land navigation of somewhere well mapped is really not so hard.  Even walking a pedometer, altimeter and map did a pretty good job if you were on a marked path, with nearby observations and a compass when you were not sure.

GNSS becomes more vital somewhere where you dont have a map, or a featureless sea, desert,  or in the air with no ground visibility.

B

What about Uber drivers whose livelyhood depends on GPS? I recently took an Uber on a rather long route. How frustrating. Several times we passed an intersection where, if I was drioving, I would have turned off to go directly to my destination. But the uber driver followed a long round about route with heavy traffic. He obviously did not have a clue where he was going and relied on his phone on the windscreen.

I have just thought......   do the black cab drivers in London stll take the "knowledge" or do they use gnsss?

David C