5.A.iii. DEM for Japan
* Primary reference citation for all data from this source
The Geographical Survey Institute (GSI) of Japan has two series of DEMs: a 50-meter grid based on 1:25,000-scale maps (in progress), and a 250-meter grid also based on 1:25,000-scale maps (completed). The data are in Japan's standard projection. The horizontal datum is the Tokyo datum; the vertical datum is mean sea level of Tokyo Bay. Both versions are copyright, based on the Survey Law in Japan.
The Digital Map 250m Grid Elevation data set was produced by manually measuring elevation values at approximately 250m intervals from 1:25,000 scale topographic maps. The actual intervals were 11.25 arc-seconds of longitude and 7.5 arc-seconds in latitude. These intervals correspond to a 40 x 40 division of one 1:25,000-scale GSI Topographic Map sheet, which covers 7.5 minutes in longitude and 5 minutes in latitude. The contour interval of these source maps is 10 meters. The source maps were derived from 1:40,000-scale stereoscopic aerial photographs, using 9 inch (23cm) film size and a lens of 6-inch (150mm) focal length, and using traditional stereoplotting techniques. Japan has large amounts of mountainous terrain, and about 65% of the land surface is forested. However, experienced operators are skilled at recreating the ground surface elevation despite these obstacles.
GSI reprojected and resampled the Digital Map 250m Grid Elevation data to WGS84 horizontal datum, with vertical datum kept at mean sea level (for Tokyo Bay), and averaged the resultant 11.25" x 7.5" data to a 30" latitude-longitude grid. It considers the vertical accuracy to be 5 to 10m RMSE.
GSI contributed these data for unrestricted use by the international scientific community, giving a copy to NGDC for GLOBE.