Determining contexts of mobile devices. Particular embodiments described herein include machines that determine two estimated positions of a mobile device that respectively correspond to first and second locations at first and second times, acquire sets of terrain or structural information for first and second areas that respectively include the first and second estimated positions, use the acquired sets of information and the estimated positions to determine if the mobile device was near or within a structure at the first and second times, determine one or more values that are indicative of vertical movement by the mobile device during a period of time between the first time and the second time, compare the one or more values to one or more threshold conditions, and determine a context of the mobile device based on the comparison.