Abstract
An Asia-Pacific type world map (a world map with East Asia-Oceania in the center) is frequently used in East Asian countries. The arrangement of continents in this map is quite different from that in an European type world map (the world map with EuropeAfrica in the center). Roughly speaking, the former is centrifugal and the latter is centripetal. Nevertheless, Asia-Pacific type world maps have been arranged in the network prepared for the European type world map without being conscious of such difference between the two.
The author, from the viewpoint that the Asia-Pacific type world map should be constructed taking due consideration of its feature, proposed a new projection suitable for this kind of map. In constructing a new projection, the following points were taken into account:
A) To maintain equal-area property
Geographers are usually interested in the size of regions and their comparison. If the equal-area condition is disregarded, less deformational projection can be obtained than equivalent projection. In this case, however, misconception of areal expansion may be brought about in almost all parts of the map. The true shape of geographical feature can be restored with the aid of graticule on the equivalent projection. On the contrary, there is no means to find the clue to know the areal error in “Pseudo-equivalent projection”. Namely, the loss of area cannot be compensated for the profit of shape. In this connection, the consideration is limited to the equivalent projection.
B) To use straight line for paralells
Straightness of paralell is too primitive condition, but this is very important character from the geographical point of view, since azonal factors in zonal phenomena, such as climate, soil, vegetation, etc. can be read more easily. Therefore, this merit should, not be despised. In the Asia-Pacific type world map where continents are dispersedly shown, room for selection by the author is restricted to, the case of pseudo-cylindrical projection.
C) To use ellipse for meridians
Whatever curves may be employed for meridians, the difference of deformational volume is very small, when the ratio of pole to the equator is fairly large. The author uses elliptic curves for meridians in the present case which is the first of his consecutive studies.
The author established the following conditions in advance of constructing a new projection:
I) The ratio of a mapping equator to the true one
The mean value of mapping equator in the existing equivalent flat-polar projections is slightly over 86% to the true equator. This is not foreign to the fact that African continent is located in the center of the map.
When Africa is shifted from the center to the edge of the map, it is perceived that north-south stretching of Africa gradually disappears in spite of increasing deformation. Such an optical illusion can be explained as follows: Defomation is emphasized visually in case where principal axes of an indicatrix coincide the direction of graticule and vice versa. Accordingly, the direction of deformation is important as well as its volume.
The author introduces this illusive effect into the Asia-Pacific type world map where no land mass exists in the center, estimating the mapping equator at 85% to the true equator. II) The ratio of north pole to the equator
When the ratio of pole to the equator is increased as far as about 60%, the merit of being able to use four corners of the map can be obtained. The utilization of four corners, as is generally known, was put into practical use in Russian world maps after the World War II. This feature will be an important key to evaluate projection in the near future.
The ratio of north pole to the equator of the new projection is estimated to be at 2/3 soo as to remedy the excessive deformation in mid-latitude margins.
