Most write-ups about location-based games stop at the fun part: you turn up somewhere, match what you see with your camera, and the next spot unlocks. I work on exactly that kind of app — Ping Hunt generates a hunt near you, walks you to real locations by GPS, and checks the scene against your camera.

Here are the problems that actually cost us time, and what we learned solving them.

1. GPS accuracy is a distribution, not a number

The most common bug report in a location game is "it says I'm at the right place but won't unlock" .

Android's Location.getAccuracy() is a radius of confidence in metres, and it is rarely what people assume. On a phone sitting flat on a café table you will often see 5–20 m of horizontal accuracy.…