Particular embodiments of a mobile device periodically detect signals transmitted by multiple fixed-location signal sources within a bounded area. A signal-location mapping is created based on the detected signals and their signal strength levels at the relative positions of the mobile computing device within the bounded area. The signal-location mapping may be created by generating a spatial distribution of signal strengths throughout the bounded area. Once the signal-location mapping has been created, particular embodiments may identify a relative position of a second mobile computing device with respect to the environment using the map of spatial distribution of signal strengths in accordance with a detected second spatial distribution of signal strengths.