April 19, 2018 -- You might have noticed a problem when you try to use your smartphone to navigate a big city: your GPS location is usually super inaccurate. Sometimes it's only by a few feet, but if you’re in a particularly dense part of the city where satellite signals are blocked by high-rise buildings, the discrepancy can be orders of magnitude greater. For most people, it’s just one of the many modern-day nuisances of urban life. But for companies that rely on two people with smartphones finding each other in a labyrinth of steel and concrete — like Uber — GPS inaccuracy is a source of never-ending pain and frustration.