Editing USGS DEM (section)

==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.
{|class="wikitable"
|-
!DEM level
!DEM series
!Production process
!Comments
|-
!Level 1
|7.5-[[minute of arc|minute]]<br>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 [[hypsography|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-[[photogrammetry|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
|}