PURPOSE: To reduce data quantity which should be prepared, to make access at high speed and to continuously change magnifications by constituting map information of plural magnifications and plural maps corresponding to the magnifications, dividing the maps into plural hierarchical levels corresponding to the priority degree of displays and switching the maps and the hierarchical levels according to the magnifications.

CONSTITUTION: The map information is constituted of plural magnifications and plural maps corresponding to the magnifications. The maps are divided into plural hierarchical levels corresponding to the priority degree of the displays. The maps and the hierarchical levels are switched in response to the magnifications. Thus, data is divided by the hierarchical levels at every mesh. When the magnification is changed in a range where data of each mesh is used, the maps are controlled to be displayed or not according to the hierarchical levels. As the magnification of the display becomes bigger and the degree of details increases, information whose priority degree is low is successively displayed as well as information whose priority degree is high. Therefore, data quantity can be reduced and the magnifications can be changed continuously or by fine steps at high speed.