That might work for a bus out in the open, but GPS doesn't work well with a lot of nearby tall buildings, or for subways underground. Maybe they are using GPS

That might work for a bus out in the open, but GPS doesn't work well with a lot of nearby tall buildings, or for subways underground. Maybe they are using GPS and silently failing in all other situations? My point is that it's nice when it works but could use some improvement on whatever method they're using.