Three-dimensional terrain-information generating system and method, and computer program therefor

A three-dimensional terrain-information generating system extracts a road region from altitude information arranged on a two-dimensional plane and adjusts the position and scale by matching the road region with a building/road map. Altitude information of a road region with a width that is greater than or equal to a preset width is obtained from the building/road map, and the obtained altitude information is arranged in a three-dimensional space. Ribbon forms that may intersect one another at a plurality of points are generated. Altitude information of a region such as a park that is almost free from the effects of a building on the three-dimensional terrain is obtained from the building/road map. Subsequently, a surface including such altitude information is created, thereby generating three-dimensional terrain data.