Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for obtaining i) historical location data specifying geographic locations of the user over a period of time that is included in a user profile of the user and ii) predefined geographic location data specifying a predefined geographic location of the user that is included in the user profile of the user; identifying a pair of cross-contaminated geographic regions that both include geographic locations specified by the historical location data of the user profiles for each of a threshold number of users of the plurality of users, and in response, merging the pair of cross-contaminated geographic regions to define a merged geographic region; and merging the merged geographic region with additional geographic regions until a cross-contamination between a resulting merged geographic region created by the merging and other geographic regions is reduced to a specified level of cross-contamination.