1. A three-dimensional map display system that displays a three-dimensional map, the system comprising: a drawing map database that is used to draw the three-dimensional map; and a display controller that refers to the drawing map database and displays the three-dimensional map as a bird's eye view from a viewpoint position looking down from a height in a gaze direction, wherein the drawing map database includes: feature polygon data for feature polygons representing shapes of features to be drawn in the three-dimensional map; and shading wall polygon data for shading wall polygons so as to provide shading in the three-dimensional map, each of the shading wall polygons being a virtual plate-like polygon having a first surface and a second surface opposite to the first surface, the plate-like polygon being arranged perpendicular to or inclined to a feature polygon, only one of the first and second surfaces being set to be visible while the other being set to be transparent, and wherein the display controller displays only the one of the first and second surfaces which is set to be visible as the shading wall polygon in the three-dimensional map.