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5.A.iii. DEM for Japan

Primary Developer: tab Geographical Survey Institute (GSI)
Title: tab 30" DEM for Japan
Publication Date: tab 1995
Bibliographic Citation: * Geographical Survey Institute, 1995. 30 Arc-second Digital Elevation Model of Japan. Geographical Survey Institute, Tsukuba, Japan (in GLOBE Task Team and others, 1999).
Post-processing: tab None
Source/Lineage Category: tab 9

* 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.

mean icon Cell-centered registration, mean of source 7.5" x 11.25" grid cells in output 30" cell.

Graphic describing georeferencing and sampling for the DEM for Japan.

plate14a icon
Plate 14.

plate15a icon
Plate 15.

Click on each image
to view larger size.

tab Plates 14 and 15 both show the DEM for Japan; with linear and semi-logarithmic scaling, respectively. Surprisingly, for data derived from cartographic sources, a histogram of this DEM is almost unnaturally smooth, and is linear between 200m and 2900m. It shows only one prominent spike, at 85m. This spike corresponds to Lake Biwa, just northeast of Kyoto. This suggests a very dense distribution of contours, little "artistic license" taken in creating the original map contours from source materials, and highly appropriate "contour-to-grid" conversion techniques in making the DEM from the cartographic source.

There appear to be a few, very subtle, breaks in topographic style in a pattern that suggests edge effects in source maps, or in contour-to-grid creation of the DEM. These may reflect subtle discontinuities in horizontal or vertical datum that affected the data when reprojected. GSI notes that slight initial discrepancies occur during the production of topographic maps, but that these are adjusted to ensure continuity between sheets (and thus in DEMs derived from them).


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