Abstract: A reference point determinator determines, as a reference point, the center of each pixel where a sloped line is located. A candidate line generator generates candidate lines each connecting between a point in a pixel having the start point of the sloped line extracted by an endpoint extractor, and a point in a pixel having the end point of the sloped line. A candidate line selector selects a candidate line having the smallest sum total of distances between the candidate line and the reference points from the candidate lines generated by the candidate line generator. A data corrector corrects the sloped line to the candidate line selected by the candidate line selector.

Abstract: A map display device includes a map polygonization unit 5 for converting a map to be displayed before display switching and another map to be displayed after the display switching into polygons having the same phase structure as each other, a triangulation unit 6 for dividing each of these polygons into triangles which make corresponding points between the map to be displayed before the display switching and the other map to be displayed after the display switching have an equal connection relation, and a morphing unit 7 for, when morphing a map display to perform the display switching, creating map data about an intermediate map having the same phase structure as each of the map to be displayed before display switching and the other map to be displayed after display switching.