Comment by tecleandor
11 hours ago
Fun thing (?), I was excited on my last trip to Japan so I could test QZSS with my Pixel 9a, that supports it, and my GPS experience in urban canyons, specially in Shibuya, was terribly bad.
Even when in GPS Test or GPS Lock tools it was showing better than 3 meter horizontal accuracy, and a multitude of locked satellites, including some QZSS, the location would usually be 30 to 50 meters away. The first days I though I had lost all my capacity to navigate Tokyo, then I noticed the GPS was gas-lightning me.
I tried removing the phone case, changing GPS settings... and I had no luck.
Extra satellites only have the potential to help a little bit in urban environments by increasing the odds of having a satellite directly overhead. Dense urban environments will have high multipath(longer time for signal to get to the receiver due to bouncing off buildings) which causes the position to be inaccurate.
They hand waved over a lot of it. The improvements in the urban canyon are not coming from GPS, but from things like wifi and 3d mapping, probably including cellular triangulations.