A communications network for GPS systems is configured so that the service area (i.e., the geographical area to which GPS service is provided) is divided into relatively small sections. Each section has a unique code assigned to it. The satellites of the GPS system transmit the GPS "base data" in the standard manner, which is then processed by a conventional reference GPS network to determine the aiding data. The communications network receives the aiding data determines differential data corresponding to each section. The communications network includes communications base stations that are distributed through the service area, which broadcasts the aiding data and the differential data to the sections. Each communication base station also includes the code of the section in which it is located. Thus, a remote unit in a given section will generally receive transmissions with the code corresponding to the section in which the remote unit is located. Using the received code, each remote unit uses the differential data corresponding to the section in which it is located to calculate pseudoranges, which are used to determine the remote unit's location.