> the GPS position is frequently wrong when you're moving between cell towers , and can be lost for several seconds in cities. You seem to be thinking of cell

> the GPS position is frequently wrong when you're moving between cell towers , and can be lost for several seconds in cities. You seem to be thinking of cell tower triangulation, not GPS. I do agree that GPS also does not do particularly well in areas with large buildings: it needs a clear view of the sky which can be hard to come by when there's skyscrapers everywhere.