GSDA:Obtaining DEM Data from the USGS
Obtaining a DEM directly from WMS
The WMS get data tool and the get data from map button allows you to download elevation data at various resolutions for anywhere in the world. The WMS developers recommend using this tool to bring elevation data into WMS. For more information about these tools and the possible data sources available using these tools, visit the Import from web information page on this wiki.
DEMs from USGS websites
The DEMs distributed by the Seamless Data Distribution System (SDDS) can be downloaded in several different formats. WMS users should choose to download data in either the Gridfloat or BIL formats, as WMS supports these formats.
The 1:250,000 scale DEMs are downloaded in the native USGS *.dem format and have a resolution of approximately 90 meters.
Obtaining a DEM from the NED (National Elevation Dataset)
- Go to the SDDS-Enhanced website at http://seamless.usgs.gov, or select the "DEM Data from USGS Seamless Map" link.
- Click the appropriate titled image on the right, such as, View and Download United States Data.
- Zoom in on the desired area by either single clicking or drawing a bounding box around the area you wish to view.
- Continue to zoom in on the map until the desired region is displayed.
- HINT: To better recognize locations, you can turn on the display of various layers, like GNIS Cities, County Labels, and Streams. These layers are located to the right of the map window. Once selected (or de-selected) the map will automatically update.
- NOTE: As you zoom in closer more layers become available for display. Some layers like GNIS Cities and Interstates are defaulted on.
- Select the Extract Box tool , which is also located on the left-hand side.
- Drag a bounding box around the area of interest.
- NOTE: Upon completing the extraction box, the order will be immediately processed. After a few moments a new page will appear with a summary of your request.
- On the SDDS Request Summary Page, click the Modify Data Request button.
- Make sure the NED 1 Arc Second dataset is checked and select Gridfloat for the data format box.
- NOTE: If the data format box does not initialize, un-select and re-select NED quickly. A sure-fire way to fix this glitch is to select the dataset, click the Save Changes & Return to Summary button, then retry the Modify Data Request button, the data format box should be available.
- Click the Save Changes & Return to Summary button.
- Click the Download button located to the far right of the NED row.
- When prompted, choose to save the zip file to disk.
- Decompress the zip file (need help decompressing?).
The DEM has now been successfully obtained, and it is ready to be read into WMS.
Obtaining a 1-degree (1:250,000 scale) DEM
- Choose the Click Here button next to "to obtain 1:250K (~90m) DEM data from..."
- Click on an area of the US map that you're interested in. You should now see a map with black squares drawn over it - each representing a 1:250,000 quadrangle.
- NOTE: Usually you'll only need to click once to zoom into a final map displaying 1:250,000 scale quadrangles from which to choose.
- Click on the quadrangle you need.
- A list of downloadable files will now be displayed.
- NOTE: Each 1:250,000 quadrangle is normally divided into two parts: East and West. Both parts should be offered in a compressed and uncompressed format.
- Select the format of your choice and proceed with the download by saving the file to your computer.
- HINT: It is best to get the compressed file, much shorter download time. For help on decompressing, click here.
- Decompress the file.
- NOTE: Unlike 7.5-minute DEMs, the 1-degree DEMs are not usually in SDTS format and have only one DEM file associated with them. You have successfully obtained the DEM, but may need to download more than one DEM to completely cover your watershed. Don't forget to format (if necessary) the DEM data before importing them into WMS.
To access a list of states instead of the Graphical Map click here.