A method is used to develop and maintain a user's lifetrail, which is a historical record specifying the location of the user while in possession of a mobile communication device. A mobile device determines its current location by extracting a beacon ID from a signal source and transmitting it to a remotely-located server, which accesses a look-up table to find the corresponding location of the signal source represented by the beacon ID. The location may be specified in accordance with a spatial compression technique. The server transmits the signal source location back to the mobile device so that the mobile device knows that it is located within the coverage area of the signal source. Battery power is conserved by collecting the beacon IDs when it is receiving the beacon signals for some other purpose and not necessarily solely for the purpose of determining its current location. Battery power can be further conserved by deferring the resolution of the beacon IDs so that they are not necessarily associated with their corresponding location when they are received, but only at some later convenient time. In some cases resolution of the beacon IDs may be performed using social graph data received from a social network.