US Patent 7831389 Map evaluation system and map evaluation method

An absolute position detector of a navigation device detects an absolute position of a vehicle. An on-map position of the vehicle is acquired based on the detected absolute position to be on a road map indicated by map data stored in the navigation device. Absolute positions detected by the absolute position detector are stored in association with on-map positions acquired based on the detected absolute positions as travel track information when the vehicle travels. An error of the map data as a reliability degree of the map data is set by comparing the travel track information with the map data.