Navigation apparatus, methods, and programs merge and correct a plurality of types of past traffic information. The apparatus, methods, and programs may store a plurality of types of past traffic information, each type of past traffic information having a priority and may merge the stored past traffic information in accordance the priorities. The apparatus, methods, and programs may detect adjacency relationships among the plurality of links; and, if a detected link number indicates that the corresponding link is not adjacent to adjacent links, replaces the detected link number for the link, the replaced link number indicating that the link is adjacent to the adjacent links.