METHOD FOR PLOTTING MAP

PURPOSE: To execute processing to plot maps at a high speed. CONSTITUTION: A processing program of a processor 7 for plotting is previously stored in a ROM 9 and a coordinate transformation program capable of simultaneously transforming the longitude and latitude coordinate arrays of one map graphic to dot coordinate arrays with one time of call instruction is included therein. The processor 7 for plotting plots map images on a video RAM 8 in accordance with the map data read out of a CD-ROM 2 to a RAM 5 and plots the map images by map graphic units of lines, polygons, etc., at this time. More specifically, the coordinate transformation program is called once for the map graphics expressed with the element points of the lines, polygons, etc., by the longitude and latitude coordinate arrays and the longitude and latitude coordinate arrays are simultaneously transformed to the dot coordinate arrays on the video RAM 8. The map graphics are then plotted on the video RAM 8 by using the dot coordinate arrays after the transformation. The similar processing is repeated with the respective map graphics.