For map data, a road system is represented by using node data, which is information concerning nodes representing points along a road, and link data, which is information concerning a link representing a road between the points. A link row is a series of links representing a series of roads in a road system, and as link row data, link data for the links that constitute the link row are arranged in the order in which the links are connected. The node data for the individual nodes of the road system are provided separately from the link row data, and to identify nodes, node identifiers are provided for the nodes of the road system. The link data includes information indicating a node identifier for a node that is located at one link end defined in the direction of the link row.
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