Actually, I was part of a team that built a GPS based walking navigation system for the blind (Google Microsoft Cities Unlocked). The limits of 5m accuracy wer

Actually, I was part of a team that built a GPS based walking navigation system for the blind (Google Microsoft Cities Unlocked). The limits of 5m accuracy were an incredible danger that prevented us from doing any u assisted trials. Even highly trained and skilled cane users would wander into the roadway usually within 10-15 minutes of using the system, purely because of GPS drift. And forget about ever using it in urban centers. In London, Boston and NYC it was rare to be more accurate than 50-100m. It's scary how bad GPS accuracy really is.