How phone GPS recording actually behaves

Plain explanations of the things that actually go wrong when a phone records where you went — and how to tell whether the app in your pocket handles them. Written to be useful whether or not you ever install this one.

• Does GPS work without a signal, or in airplane mode?

  Yes — and the reason why explains most of what people find confusing about phone navigation. Your phone works out where it is by listening, not by asking. What a data connection actually buys you is speed and a map.

• What should a GPS recorder do when the signal drops?

  Every tracker meets a tunnel eventually. The difference between them is what they write down about the part they could not see — and the common answer, a straight line across the gap, is a number the app cannot stand behind.

• Why GPS elevation gain is wrong, and what a barometer fixes

  Vertical is the weakest thing a satellite receiver measures, and the way climb is totalled turns that weakness into a large, always-positive error. Why a pressure sensor is the better instrument, and where it fails too.

• Recording GPS in the background on iOS without losing the ride

  iOS can suspend or terminate your recorder at any moment and owes you no warning. What that means for an app that is supposed to be writing down where you went, and what actually protects a ride.

• Getting your rides out: GPX, KML and CSV, and what each is for

  Three formats, three different jobs. What each one actually contains, which to pick for which task, and why being able to export at all is the property that decides whether your riding history is yours.