A storage medium for map information for a navigation system includes an IC memory chip or an IC memory card of a small memory capacity. This storage medium stores detailed map information of a limited region including part of a highway network and information of the highway network covering a predetermined area which includes the limited region and is wider than the limited region. A system for offering map information for a navigation system includes two storage media. One storage medium is the same as the above-mentioned storage medium and the other storage medium has a small memory capacity. The other storage medium stores detailed map information of a limited region different from the limited region whose information is stored in the one storage medium.