USGS DEM - DEM Level

A USGS DEM can be classified into one of four levels of quality. This is due to the multiple methods of data collection, and certainty in the data.

DEM level	DEM series	Production process	Comments
Level 1	7.5-minute 30-minute	Created by autocorrelation or manual profiling from aerial photographs	May be derived from a wide variety of sources using any of a number of USGS approved techniques and instrumentation
Level 2	All series	Created from digital line graph (DLG) contours or equivalent, from any USGS map series up to 1:100000 scale	The accuracy and data spacing are intended to support computer applications that analyze hypsographic features to a level of detail similar to manual interpolations of information from printed source maps
Level 3	7.5-minute	Created from DLG that have vertically integrated with all categories of hypsography, hydrography, ridge line, break line, drain files, and all vertical and horizontal control network	Requires a system of logic to interpret the data
Level 4	All series	Created from electronic (non-photogrammetric) imaging sensor systems, either active (e.g., radar or lasar) or passive (received radiant energy)	The process includes all additional post-processing required to bring the DEM grid to its final form

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“For him nor deep nor hill there is,
But all’s one level plain he hunts for flowers.”
—Unknown. The Thousand and One Nights.

AWP. Anthology of World Poetry, An. Mark Van Doren, ed. (Rev. and enl. Ed., 1936)