The location of a wireless mobile device may be estimated using, at least in part, one or more pre-existing Network Measurement Reports (“NMRs”) which include calibration data for a number of locations within a geographic region. The calibration data for these locations is gathered and analyzed so that particular grid points within the geographic region can be determined and associated with a particular set or sets of calibration data from, for example, one or more NMRs. Sets of grid points may be evaluated as a function of parameters of the calibration data, and a set of grid points may be selected as a function of a predetermined criteria. The location of a mobile device in the geographic region may then be determined as a function of the predetermined criteria.