Navigation system

A navigation system for detecting a present position of a movable body and performing a navigation for the movable body on the basis of map information, said navigation system comprising:

• a storage device of non-volatile type capable of writing the map data thereinto and reading the map data therefrom;
• a map data transferring device for obtaining the map data corresponding to a predetermined area, and transferring and storing the map data corresponding to the predetermined area to said storage device;
• an empty area judging device for judging whether or not an empty storage area having a predetermined capacity is reserved in said storage device when said map data transferring device is to transfer the map data corresponding to the predetermined area to said storage device;
• and
• an erasing device for determining unnecessary data among data stored in said storage device on the basis of a predetermined condition, and erasing the unnecessary data from said storage device if said empty area judging device judges that the empty storage area is not reserved, said erasing device determines the unnecessary data among the map data transferred and stored in said storage device, wherein said erasing device determines the unnecessary data on the basis of management information, which is correlated with the map data stored in said storage device, the management information comprises the number of accesses for the map data stored in said storage device, and said erasing device determines the map data, the number of accesses for which is the minimum, as the unnecessary data.

A navigation system for detecting a present position of a movable body and performing a navigation for the movable body on the basis of map information, said navigation system comprising:

• a storage device of non-volatile type capable of writing the map data thereinto and reading the map data therefrom;
• a map data transferring device for obtaining the map data corresponding to a predetermined area, and transferring and storing the map data corresponding to the predetermined area to said storage device;
• an empty area judging device for judging whether or not an empty storage area having a predetermined capacity is reserved in said storage device when said map data transferring device is to transfer the map data corresponding to the predetermined area to said storage device;
• and
• an erasing device for determining unnecessary data among data stored in said storage device on the basis of a predetermined condition, and erasing the unnecessary data from said storage device if said empty area judging device judges that the empty storage area is not reserved, said erasing device determines the unnecessary data among the map data transferred and stored in said storage device, wherein said erasing device determines the unnecessary data on the basis of management information, which is correlated with the map data stored in said storage device, wherein the management information comprises date and time of access for the map data stored in said storage device, and said erasing device determines the map data, the date and time of access for which is the oldest, as the unnecessary data.

A navigation system for detecting a present position of a movable body and performing a navigation for the movable body on the basis of map information, said navigation system comprising:

• a storage device of non-volatile type capable of writing the map data thereinto and reading the map data therefrom;
• a map data transferring device for obtaining the map data corresponding to a predetermined area, and transferring and storing the map data corresponding to the predetermined area to said storage device;
• an empty area judging device for judging whether or not an empty storage area having a predetermined capacity is reserved in said storage device when said map data transferring device is to transfer the map data corresponding to the predetermined area to said storage device;
• and
• an erasing device for determining unnecessary data among the map data transferred and stored in said storage device on the basis of a predetermined condition, and erasing the unnecessary data from said storage device if said empty area judging device judges that the empty storage area is not reserved, wherein said erasing device determines the map data corresponding to an areal block, which is farthest from the present position, as the unnecessary data,
• wherein the map data comprises a plurality of block map data for each unit block obtained by dividing a whole map into unit blocks.