The CNS Research Laboratory (URE-CNS) of the ENAC, in collaboration with the STNA and SEXTANT AVIONIQUE, is developing a tool for pro-viding DGPS reference stations siting guidelines for the French Civil Aviation Authority. This tool is based on computed error predictions using mathematical models, and on signal disturbance measurements made at preselected locations. The aim of the proposed paper is to present the complete siting tool which was developed along with some examples of its use showing the extent of the validity of its predictions.