In a virtual three-dimensional space, an overhead image of a region in the virtual three-dimensional space is shot by a virtual camera provided in the virtual three-dimensional space. Next, it is determined whether or not the information about a color included in the shot overhead image satisfies a predetermined condition. Image data of the overhead image which it is determined in the result of the determination does not satisfy the predetermined condition is accumulated in a predetermined storage medium, thereby generating resource data. The above processing is repeated until all overhead images corresponding to a predetermined region in the virtual three-dimensional space are shot.
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