Systems, methods, and programs acquire map information including road width data and background type data. The systems, methods, and programs acquire altitude information indicating an altitude of each unit region, the unit region being set by dividing a map indicated in the map information into a plurality of unit regions having a predetermined size, and calculate a predicted altitude of each of a plurality of reference points based on the road information and the altitude information, the plurality of reference points being set along a road. The systems, methods, and programs determine a predicted altitude reliability of each of the reference points based on at least one of the background type data and the road width data at the position of the each of the reference points.