Map image display system, map image display device, map image display method, and computer program

A map image display method comprising:

• acquiring map data that is divided into a plurality of areas and hierarchically structured into a plurality of layers based on an amount of road network information;
• defining a display target area on a display device based on the acquired map data;
• dividing the display target area into a plurality of division areas with parts of neighboring ones of the division areas overlapping each other;
• generating a map image for each of the division areas, each map image being based on a different layer of the map data;
• in an area where two or more of the generated map images overlap, gradually changing a transmittance of a first one of the overlapped map images so that a transmittance of an outer portion of the first overlapped map image becomes higher than a transmittance of an inner portion of the first overlapped map image;
• displaying a second one of the overlapped map images on the display device;
• and
• after the second map image is displayed on the display device, displaying the first map image on the display device so that the first map image is overlapped on the displayed second map image.

A computer-readable storage medium storing a computer-executable image display program, the program comprising:

• instructions for acquiring map data that is divided into a plurality of areas and hierarchically structured into a plurality of layers based on an amount of road network information;
• instructions for defining a display target area on a display device based on the acquired map data;
• instructions for dividing the display target area into a plurality of division areas with parts of neighboring ones of the division areas overlapping each other;
• instructions for generating a map image for each of the division areas, each map image being based on a different layer of the map data;
• instructions for, in an area where two or more of the generated map images overlap, gradually changing a transmittance of a first one of the overlapped map images so that a transmittance of an outer portion of the first overlapped map image becomes higher than a transmittance of an inner portion of the first overlapped map image;
• and
• instructions for displaying a second one of the overlapped map images on the display device;
• instructions for, after the second map image is displayed on the display device, displaying the first map image on the display device so that the first map image is overlapped on the displayed second map image.