1. A method of estimating demographics associated with a selected geographic area, comprising: for each mobile device of a plurality of mobile devices, associating a more recent location estimate of the mobile device determined by a positioning system that is within the selected geographic area with a previous location estimate of the mobile device determined by the positioning system, and determining an origin geographic area that includes the previous location estimate; estimating demographics associated with the selected geographic area, by a computer system, based at least in part on demographics associated with the origin geographic areas of the plurality of mobile devices; and transmitting the estimated demographics to at least one other computer system.