Digital Elevation Models (DEM)
Please Note: For a more comprehensive and updated discussion about elevation data, see the Elevation Data Sources website. This DEM website remains active for purposes of documenting older, superceded DEM data which were acquired many years ago and are still available on the Geodata Server.
The USGS Digital Elevation Model (DEM) data files are digital representations of elevation information in a raster or grid form. DEMs consist of a sampled array of elevations for a number of ground positions at regularly spaced intervals. These digital cartographic/geographic data files are produced by the U.S. Geological Survey (USGS) as part of the National Mapping Program and are available for the entire US from the USGS National Map.
The entire United States has DEM coverage at 30 meter resolution (1 arc second), and much of the country is available at 10 meter resoultion (1/3 arc second). The National Elevation Dataset (NED) is a regularly updated composite of the latest DEM data for the country, and represents the most current and highest resolution DEM data available that USGS has produced. Often DEMs may be found which are tiled by 7.5 minute quadrangles or some other tiling scheme. For more information see the USGS Digital Elevation Model Data Guide or the NED FAQ's.
Downloading DEM Data from the Web
The USGS maintains a DEM download website at at: http://edc.usgs.gov/geodata/.
Many of the downloads are in SDTS (Spatial Data Transfer Standard) format. SDTS was developed by the federal government as a non-proprietary format for electronic transfer of spatial data (see the SDTS Web Site for more information). The SDTS DEM data must be converted using one of a number of different tools (see the SDTS translator software site). ESRI's ArcGIS has built-in SDTS conversion utilities. See the Help documentation or other online sources for more information.
If you are not sure which quads you need to download, load the 1:24,000, 1:100,000 or 1:250,000 quad neatline data sets into your GIS software (see: Quad Neatline data) or see the interactive North Carolina topographic map indexes accessible from the North Carolina Geological Survey.
DEM Data Available to NCSU
USGS has produced 10 meter (1/3 arc second) DEM rasters for most portions of Western NC (see image at right). These DEMs are available for NCSU download and use from the Geodata server. See the GIS Lookup Record for access instructions. Non-restricted access to this data in SDTS format (free) and other formats is available at mapmart.com.
For generalized elevation mapping of North Carolina and the Southeast US, these DEMs are available on the Geodata server:
- A seamless NED raster for North Carolina is available with 30 meter resolution based on 1:24,000 scale. It was obtained in August, 2000 and does not incorporate the Western NC 10-m DEMs or other DEM improvements since that time. It is an Arc/Info .e00 file projected in Stateplane NAD83 meters, and in a 615 MB zip file saved at /fedgov/usgs/ned/ned_nad83m.zip.
- A 1:250,000 scale DEM data is also available for North Carolina as a statewide seamless mosaic at /dem/nc250. Filesize is 122 MB.
- Southeast US 1:250,000 DEMs are available at /dem/SEUSdems/ for South Carolina, Georgia, Tennessee, and Mississippi.