The method herein described is based on the principle of shading by oblique illumination. In working out this new method, however, the author investigated theoretically the intensity of light and shade or the configuration of brightness on a surface, and found a way of correctly representing on a map the brightness thus determined, justifying his view that the reasoning of the investigation should be based on realities, and that the method of drawing should be as scien-tific as possible, so that the resulting map may be exact and true to nature.
The process of drawing may be explained with the aid of Fig. 3. The ground is first tinted grey, the contours in the light are then drawn in white, and those in the shade in black. The breadth of the contours, however, varies with the cosine of the angle θ between the horizontal direction of the incident ray and the normal to the contour at the point under consideration. It is shown that the configuration of brightness of the two cases, namely, the actual surface and the map, will resemble each other very closely, if the maximum breadth of the contours may be determined theoretically in terms of the brightness of the ground and of the contours.
The advantages of the proposed method are:
1. The method gives a remarkable effect of relief.
2. The process of drawing is simple and scientific, and involves no ambiguity.
3. The maps afford at a glance a clear idea of the minor featuies, no matter how complicated, they may be, to say nothing of the general character of the country.
The Association of Japanese Gergraphers