Elevation - 33 of 41
Elevation FAQs - 41 Found
3DEP standard DEMs are produced from the highest quality elevation sources within the data holdings of the USGS National Geospatial Program. As of 2015, about 25% of the conterminous U.S. coverage is from high resolution lidar and photogrammetric source, while the remainder of CONUS and Hawaii coverage is from USGS topographic map contours. About one-third of Alaska coverage is from ifsar 5-meter source and the balance is produced from topographic map contours. Quality and currency are primary factors in determining if a dataset will be ingested into the standard DEM layers. General categories of standard DEM source data are characterized below:
o High resolution source DEMs (3 meters or better) are typically derived from lidar or digital photogrammetry, and usually with edited water bodies.
o Moderate resolution source DEMs (4 to 10 meters) are typically derived from photogrammetrically produced contours or mass points and breaklines, or from ifsar. Although moderate resolution DEMs are presently the predominant source in 3DEP elevation data, they continue to be replaced as higher quality lidar and ifsar source data are acquired.
o Low resolution DEM source:
- 30 meter DEMs from 1:24,000-scale cartographic contours are only used as source in Puerto Rico and as void fill in very limited areas of the conterminous U.S.
- 2 arc-second DEMs are a standard 3DEP product over the State of Alaska. They are derived from either cartographic contours compiled at a scale of 1:63,360, or from 1 arc-second Shuttle Radar Topography Mission (SRTM) data over the Aleutian Islands.
- Bathymetric DEMs for some coastal areas are collected using lidar, sonar, and other methods of subsurface terrain measurement, transformed to a common datum, and resampled to 1/9 arc-second resolution.