Data coverage for Italy was available from SGN/NGDC, NIMA and USGS/GTOPO30. (The latter candidate had high-resolution SGN source materials, reprocessed as described in Section 5.A.iv by NGDC to 30".)
Again, data from all candidates were of relatively high quality. However, histograms of the SGN data showed significantly less spiking than those for NIMA and GTOPO30. Similarly, slope, aspect, and shaded relief analyses showed that the SGN data were of somewhat higher quality at higher elevations, but of much higher quality at lower elevations. This probably reflects a more detailed scale of SGN’s source materials, with smaller contour intervals than may have been used by NIMA to make DTED Level 1 data. In the areas of the SGN/NGDC DEM that contained holes (see Section 5.A.iv), DTED Level 0 discrete values were inserted.
Thus the SGN/NGDC DEM was selected for Italy, supplemented where it had holes by DTED Level 0 discrete values.