19. A method performed by one or more computer systems coupled to a packet-based network, comprising: receiving an advertisement (ad) request from the packet-based network, the ad request including a location indicator, the location indicator having first location components; deriving one or more second location components from one or more of the first location components and by consulting information stored in a storage device accessible by the one or more computer systems; forming one or more location component groups each including a respective subset of one or more location components selected from the first location components and from the one or more second location components, the respective subset of one or more location components being determined to be consistent with each other; and generating a spatial representation of the location of the mobile device based on the ad request, the spatial representation including one or more probable geographical areas, each of the one or more probable geographical areas corresponding to a respective one of the one or more location component groups.
22. The method of claim 19 , further comprising determining a weight associated with each respective one of the one or more probable geographical areas using historical data.