Abstract: A navigation device realizes such processing as map display and route guidance based on map data stored in a memory card. The data in the memory card tends to be volatilized with an increase in the frequency of reading of data. Therefore, the data that are highly frequently read out are held in a RAM so as to be read from the memory card at a decreased frequency. Further, the passage of time is calculated from the date and hour the data are recorded in the memory card, and the whole data in the memory card are refreshed every time when the passage of time exceeds a threshold value T1.

Abstract: A navigation device realizes such processing as map display and route guidance based on map data stored in a memory card. The data in the memory card tends to be volatilized with an increase in the frequency of reading of data. Therefore, the data that are highly frequently read out are held in a RAM so as to be read from the memory card at a decreased frequency. Further, the passage of time is calculated from the date and hour the data are recorded in the memory card, and the whole data in the memory card are refreshed every time when the passage of time exceeds a threshold value T1.

Abstract: A navigation system includes: an information center; a navigation device of a vehicle communicating with the information center; a communication unit transmitting information of a destination to the information center; a center side transmission unit searching positional information of the destination in a database of the information center and transmitting the positional information to the navigation device; a calculation unit of the navigation device calculating a first route to the destination; a navigation side transmission unit transmitting first route calculation result to the information center; and a determination unit of the information center calculating a second route to the destination, comparing second route calculation result with the first route calculation result, and determining whether the navigation device guides a route to the destination based on the first or second route calculation result.