Are the USGS DEMs the only source used in NED processing?
A. Source data for the NED are selected from the available DEMs according to the following ranking (highest priority listed first): high-resolution elevation data, 10-meter USGS DEMs, 30-meter Level 2 USGS DEMs, 30-meter Level 1 USGS DEMs, 2-arc-second USGS DEMs, 3-arc-second USGS DEMs. Note that the 2-arc-second DEMs are used only in Alaska, and the 3-arc-second DEMs are used only to fill in values over some large water bodies. The composition of the source data used in NED has a trend with 10-meter DEMs increasing and the corresponding decrease in 30-meter DEMs. Thus, the ongoing production of USGS 10-meter DEMs is reflected in each NED release. The total for 10-meter DEM source includes 777 7.5-minute quadrangle-based DEMs derived from 1:24,000-scale hypsography data over Kentucky. Although these DEMs are not standard USGS 10-meter DEMs because they were produced in a non-standard projection (State Plane), they were produced with the same method as the 10-meter DEMs and thus have th
