US Patent 7471952 Data terminal device

A position data receiving part receives position data transmitted from an artificial satellite. A wireless unit transmits and receives data with respect to a base station. A detailed map data memory part stores detailed map data received by the wireless part. Scale determining part determines the scale of the road map according to a plurality of position data received a plurality of times by the position data receiving part. A display part displays the road map of the scale determined by the scale determining part and detailed map data stored in the memory part.