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

1. A map image display system comprising:

a controller configured to:

acquire 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;

define a display target area on a display device based on the acquired map data;

divide the display target area into a plurality of division areas with parts of neighboring ones of the division areas overlapping each other;

generate 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 change 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;

display a second one of the overlapped map images on the display device; and

after the second map image is displayed on the display device, display the first map image on the display device so that the first map image is overlapped on the displayed second map image.

2. The map image display system according to claim 1 , wherein the controller is configured to:

sets an area of a map in the display target area, the set area visually recognized when viewing the map downward obliquely from a virtual point-of-view above the map;

divide the display target area into the plurality of division areas according to a distance from the virtual point-of-view; and

generate the first map image based on a division area nearer the virtual point-of-view and a layer of the acquired map data having a larger amount of road network information.

3. The map image display system according to claim 1 , wherein the controller is configured to:

gradually change the transmittance of the first map image.

4. The map image display system according to claim 1 , wherein:

the first overlapped map image includes an image indicating a background and a road shape.

5. The map image display system claim 1 , wherein the controller is configured to:

display a route image superimposed on the first overlapped map image, the route image being an image indicating a shape of a navigation route to a destination; and

change a transmittance of the route image as well as the transmittance of the first map image.

6. The map image display system according to claim 4 , wherein the controller is configured to:

display a congestion image superimposed on the first map image, the congestion image being an image indicating a congestion level of a road; and

change a transmittance of the congestion image as well as the transmittance of the map image.

7. A navigation device comprising the map image display system of claim 1 .

8. 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.

9. The map image display method according to claim 8 , further comprising:

setting an area of a map in the display target area, the set area visually recognized when viewing the map downward obliquely from a virtual point-of-view above the map;

dividing the display target area into the plurality of division areas according to a distance from the virtual point-of-view; and

generating the first map image based on a division area nearer the virtual point-of-view and a layer of the acquired map data having a larger amount of road network information.

10. The map image display method according to claim 8 , further comprising:

gradually changing the transmittance of the first map image.

11. The map image display method according to claim 8 , wherein:

the first overlapped map image includes an image indicating a background and a road shape.

12. The map image display method according to claim 8 , further comprising:

displaying a route image superimposed on the first overlapped map image, the route image being an image indicating a shape of a navigation route to a destination; and

changing a transmittance of the route image as well as the transmittance of the first map image.

13. The map image display method according to claim 8 , further comprising:

displaying a congestion image superimposed on the first map image, the congestion image being an image indicating a congestion level of a road; and

changing a transmittance of the congestion image as well as the transmittance of the map image.

14. The map image display method according to claim 8 , wherein the method is executed by a controller.

15. 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.

16. The computer-readable storage medium according to claim 15 , the program further comprising:

instructions for setting an area of a map in the display target area, the set area visually recognized when viewing the map downward obliquely from a virtual point-of-view above the map;

instructions for dividing the display target area into the plurality of division areas according to a distance from the virtual point-of-view; and

instructions for generating the first map image based on a division area nearer the virtual point-of-view and a layer of the acquired map data having a larger amount of road network information.