The map data may be updated on a specified area basis. This may shorten the time for updating the map data as well as lowers the cost of map data update. A navigation system comprising a data center 51 for distributing map data about a designated area upon receipt of a data-distribution request; an on-board device 14 having a data storage that stores map data, for updating the map data about the designated area with new map data distributed from the data center; and wherein the map data distributed from the data center has a layered structure in which the map data in a lowest-layer represents the designated area while the map data in a higher-layer represents a wider area that includes a smaller area represented by a lower-layer map data.