1. A map update apparatus comprising: an image display device; a storage medium configured to store map data that is classified into several unit areas, which include a first unit area and a second unit area adjoining the first unit area, the first unit area containing a first border node, the second unit area containing a second border node, the first border node and the second border node having an identical position on a unit areas border that is a border between the first unit area and the second unit area; and a control circuit configured to cause the image display device to display a map based on the map data, the control circuit comprising: an updating section configured to update the second unit area; a determining section configured to execute a determination as to whether or not a position separation occurs, after the updating by the updating section, in between a position of the first border node and a position of the second border node; and a moving section configured to move the positions of the first border node and the second border node to a target point that is on the unit areas border between the first unit area and the second unit area so as to make identical the positions of the first border node and the second border node, based on an affirmative result of the determination by the determining section.