GSDA:DEM
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Digital Elevation Models Representing Topography and Terrain
USGS Seamless Map
Obtain Data from USGS Seamless Map
The USGS provides DEM datasets as part of the Seamless Data Distribution System (SDDS). The two types of data provided as part of this system include:
- Shuttle Radar Topography Mission
- 30 Meter - Data available for contiguous US, Hawaii and southern Alaska
- 90 Meter - Extensive coverage including South America and most of North America
- National Elevation Dataset (NED)
- 1/9 Arc Second - 3 meter resolution limited to select areas of Washington state
- 1/3 Arc Second - 10 meter res. available covering most of the contiguous US
- 1 Arc Second - 30 meter res. for all of the United States
- 2 Arc Second - Dataset specific for the state of Alaska
Details:
- SRTM and NED data is offered in Gridfloat, BIL, ArcGRID, and TIFF formats. (To download a DEM, select the Gridfloat type)
- You can define a custom, seamless area to download.
- The interface allows you to display various GIS layers to aid in the selection process.
- Data can be downloaded in files up to 100MB maximum size.
- Downloads are free (no cost).
USGS Earth Explorer
Download various data (including elevation) from the USGS
Details:
- Download DEM data in various formats.
- Download various land cover and vegetation data.
- Download USGS imagery.
- Downloads are free, but an account must be created to download.
NASA LP DAAC (Land Processes Distributed Active Archive Center)
Download various data collected by NASA
Details:
- Download DEM data from various sources and in various formats from around the world.
- Downloads are free, but an account must be created to download.
webGIS
Details:
- Terrain data offered
- USGS 7.5 minutes - 1:24K scale (~30 m res) <Covers all of contiguous United States>
- USGS 1 degree - 1:250K scale (~90 m res) <Hawaii and Alaska only>
- Data only available in *.dem format
- Graphical US map makes locating an area easy
- Downloads are free (no cost).
GeoBase
CGIAR-CSI SRTM 90m DEMs (Worldwide)
Worldwide DEM data in SRTM format-90 meter resolution
MapMart
Details:
- Terrain data offered
- 10 Meter SDTS (Spatial Data Transfer Standard) <Limited coverage of US>
- 30 Meter SDTS <Covers all of contiguous United States and Hawaii>
- Limit of 10 quads per download
- Graphical US map makes locating an area easy
- Downloads are free (no cost).
- The following types of formats are also available for a fee
- USGS DEM
- XVY ASCII Grid
- Arc ASCII Grid
- DXF Mesh
GIS Data Depot
SDTS DEM Data from GIS Data Depot
Details:
- Digital Elevation Model (DEM) data:
- 10 Meter Resolution
- 30 Meter Resolution
- SDTS Format
- Extensive coverage of the U.S.
- Free downloads.
- Data offered free may also be available in other formats for a fee.
Tips:
- The USGS GNIS and USGS Map Locator are useful tools to determine the name of the DEM you need.
Land Info
Details:
- Digital Elevation Model (DEM) data:
- 1:250K Resolution
- 1:24K Resolution
- Numerous formats
- *.dem
- ESRI GRID
- ESRI BIL w/HDR
- *.dted
- Downloads must be purchased
DEM Overview
Uses of DEM Data
There are many uses and applications of DEMs. GIS (Geographic Information System) software such as ArcView and ARC/INFO, as well as modeling software such as WMS (Watershed Modeling System) can use DEMs for many engineering and scientific applications. WMS uses DEM data to produce watersheds which are then used to model storm events, create hydrographs, route floods down rivers and through reservoirs, etc. This information can be used to design culverts, dams, detention basins and other hydraulic structures. DEM data are commonly used to create another type of digital terrain model called a TIN (Triangulated Irregular Network). Public domain software is available for tasks such as simply viewing a DEM -- one example is dlgv32 Pro, a tool provided by the USGS.
With powerful modeling software such as WMS, using DEM data to run a model is not difficult, and can be accomplished in four general steps:
- Find and/or download the needed DEM data.
- Import the DEM(s) into WMS
- Delineate the watershed by inserting stream networks, one or more outlets, and reservoirs. If desired, a TIN can be created as well. Additional hydrologic data such as land use and soil type can also be used in WMS.
- Run the model and view the results. WMS supports several models such as HEC-1, NFF, Rational, TR-55, TR-20, HEC-HMS, and GSSHA.
DEM Definition
A DEM (Digital Elevation Model) is simply a digital map of elevation data. These maps, a type of DTM (Digital Terrain Model), are raster data meaning that they are made up of equally sized gridded cells each with a unique elevation.
DEMs come in different scales and resolutions. For example, 1:24,000 scale DEM is simply a USGS (United States Geological Survey) 7.5’ quadrangle that has been digitized and each cell in the DEM represents a block of terrain 30 meters x 30 meters. The 1:250,000 scale DEM (also known as a 1-degree or a 3 arc-second DEM) has a resolution of 90 meters x 90 meters. DEMs with better resolution are available, but require large amounts of computer memory and disk space and are often impractical to use for large areas of land. If an individual DEM does not cover the entire area of interest, then multiple DEMs can be tiled together to make one large DEM.
The projection and datum for a DEM varies. A common projection for DEMs is UTM (Universal Transverse Mercator) coordinates (meters) and have a specific datum associated with them. Elevations are usually in meters, but sometimes are in feet for areas of low relief, and are referenced to mean sea level.
DEM Tips
- How do I obtain a DEM from USGS?
- How do I obtain a DEM from GIS Data Depot?
- How do I use the USGS Map Locator?
- How do I use the USGS GNIS (Geographic Names Information System)?
- How do I decompress data files?
- How do I import a DEM (native *.dem or SDTS format) into WMS?
- How do I import an NED Gridfloat file into WMS?
- How do I use WMS to convert data to a different coordinate system?
