Systems and methods including mobile devices determining their locations using location determination units, such as GPS receivers. Locations of the mobile devices and predefined locations/regions that have been visited by the mobile devices during a period of time are efficiently organized into a location graph that identifies the neighbors of predefined locations, distances to neighbors, and visitation counts of mobile devices to the predefined locations during the period of time. Keyword values for keywords representing user attributes are assigned to mobile devices and the predefined locations. Based on the location graph, the keyword values are propagated via the location graph, from neighbors to predefined locations, from mobile devices to predefined locations, and from predefined locations to mobile devices, to incrementally improve the accuracy of the keyword values over a number of time periods.