1. A computer-implemented method for enabling content providers to provide targeted content to users, the method comprising: accessing a first mapping that maps specific subscriber computing device IDs to corresponding segments, said subscriber computing device IDs associated with particular network users, said first mapping generated using user-specific data associated with said network users; accessing a second mapping that maps segments to corresponding geographic regions, said second mapping generated using aggregated data associated with residents of said regions; and providing a query interface that provides functionality for retrieving segment data associated with particular subscriber computing device IDs, said query interface configured to receive, from a content provider, a request that specifies a subscriber computing device ID and to respond to the request by a process that comprises: determining whether the subscriber computing device ID is mapped in the first mapping to at least one segment; when the subscriber computing device ID is determined to be mapped to at least one segment, returning, via the query interface and in response to the request, an indication of the at least one segment, to thereby enable the content provider to provide targeted content to a subscriber computing device associated with the subscriber computing device ID that is based on information specific to a corresponding user associated with the subscriber computing device ID; and when the subscriber computing device ID is determined to not be mapped in the first mapping to at least one segment, determining a geographic region associated with the subscriber computing device ID, looking up in the second mapping one or more segments associated with the geographic region, and returning, via the query interface and in response to the request, an indication of the one or more segments associated with the geographic region, to thereby enable the content provider to provide to the subscriber computing device associated with the subscriber computing device ID content that is targeted to the geographic region, said method performed by a computing system that is programmed to perform the method, said computing system comprising one or more computing devices.