5.B.i.a. Japan

Data coverage for Japan was available from GSI, NIMA and USGS/GTOPO30. The peer review Web site for GLOBE notes that the data are all of relatively high quality. However, inspection of the data for Japan helped to confirm independent peer review comments that the NIMA (DTED Level 0) "mean" values are sometimes lower than the "minima." Actual data values for all candidates tended to disagree by very little. Shaded relief, slope, and aspect images appear nearly identical, as a rule. However, the histograms of the GSI data were notably smooth, lacking the spikes common in DEMs generated from cartographic sources (and which had typical spike patterns in the GTOPO30 and NIMA versions). This suggests that a common artifact in DEMs developed from cartographic sources was addressed more thoroughly in the GSI DEM of Japan than in any other DEM from such sources ever seen by ourselves. The result is a DEM that has the smoothest distribution of elevations, and the least "binning" favoring contour values of source maps, of any candidate DEM. Thus the GSI DEM was selected for Japan.