Polygonal road network data are prepared based on road network data and city map data. The road network data include node data (905, 913) and link data (905, 917). The node data (905, 913) express respective intersections as nodes, and the link data (905, ...

An object of the present invention is to accomplish the automatic preparation of road data in which roads and intersections are expressed by polygons that show accurate agreement with the complicated road shapes on city maps. In simple polygon preparation ...