A GNSS enabled mobile device transmits to a location server a combination of GNSS-based location data and non-GNSS based location data used to determining reference positions at the location server. The GNSS mobile device receives the determined reference positions from the location server to calculate an associated GNSS position fix. The transmitted GNSS-based location data comprises GNSS position fixes associated with the GNSS enabled mobile device. The transmitted non-GNSS-based location data comprises a serving Cell-ID, neighbor Cell-IDs, neighbor cell fingerprinting, timing advance parameters, and/or a mobile country code. Reference positions associated with the serving Cell-ID are determined and/or refined based on location information acquired from each of associated mobile devices. To respond to a reference position request from the GNSS enabled mobile device without an associated serving Cell-ID, the location server determines corresponding reference positions by combing subscriber population density with an associated MCC.