TL;DR: it's just using the WiFi networks' names to decide whether you're close or not.
I thought "environmental fingerprints" were referring to something more elaborate, like a fingerprint of the local audio environment, or using the accelerometer to measure the local spacetime curvature.
I thought "environmental fingerprints" were referring to something more elaborate, like a fingerprint of the local audio environment, or using the accelerometer to measure the local spacetime curvature.