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Preliminary Validation of DCW DEM of Japan 
Hiroshi Murakami 
Geographical Survey Institute 
Japan 
The EROS Data Center of the US Geological Survey has been developing a 30arc second grid DEM 
(Digital Elevation Model) of the world (DCW DEM) by interpolating contour lines, spot heights, and 
drainage data of the DCW(Digital Chart of the World). The nominal accuracy of the DCW DEM is 
estimated to approximately +400 m RMSE. However, detailed accuracy assessment of DCW DEM 
has not been conducted with higher accuracy DEMs. The DCW DEM covers Japan where a high 
accuracy DEM is available from the Geographical Survey Institute (GSI) with a nominal post spacing 
of 250 m (GSI DEM), and the elevation accuracy of less than 30 m. The direct comparison between 
DCW DEM of Japan (DDJ) and GSI DEM was not considered to give the accuracy of DDJ due to the 
difference of the nominal geodetic coordinate system between the DEMs. However, a coordinate 
measurement of 26 triangulation points of the south-western part of Japan revealed that the geodetic 
coordinate system of the DCW of Japan is not the WGS-84, but the Tokyo Datum, on which GSI 
DEM is based. Consequently, the two DEM's were directly compared and DDJ's accuracy assessed 
without transforming the GSI DEM to the WGS-84. The resultant standard deviation of DDJ from 
GSI DEM was t 77 m, which is significantly better than the nominal accuracy of +400 m RMSE. 
This high accuracy can be attributable to the use of spot heights and drainage data of DCW for DEM 
interpolation. However, the high accuracy of DDJ may not be applicable to DCW DEM of the other 
areas of the world, because the original maps of ONC (Operational Navigation Chart) for Japan may 
have higher accuracy of those of other countries. The comparison result also showed that the 
elevation values of DDJ is larger than those of GSI DEM at lower elevations and smaller at higher 
elevations. This is reasonable considering the fact that the contour interval of DCW is about 300 m 
which is significantly larger than that of the original maps of GSI DEM (10 m contour interval).