USGS SDDS
To go directly to the NED download page, go here: http://seamless.usgs.gov/
The National Elevation Dataset (NED) is a new raster product assembled by the U.S. Geological Survey. NED is designed to provide National elevation data in a seamless form with a consistent datum, elevation unit, and projection. Data corrections were made in the NED assembly process to minimize artifacts, perform edge matching, and fill sliver areas of missing data. NED has a resolution of one arc-second (approximately 30 meters) for the conterminous United States, Hawaii, and Puerto Rico and a resolution of two arc-seconds for Alaska. More info can be found at http://gisdata.usgs.net/NED/.
SRTM 30m and SRTM 90m data is also available from the the USGS Seamless Distribution site. Information on the SRTM data can be found at http://srtm.usgs.gov/ .
How to download
The data can be downloaded at http://seamless.usgs.gov/. There is online help available by clicking help in the upper right corner.
- Click on the View and Download United States Data graphic.
- Select the Download tab on the right hand side of the display.
- Check the boxes for NED, 1/3 NED or 1/9 NED.
- Using the Zoom tool, zoom into the area you are interested in.
- Define the area by either clicking the Define Download Area by Coordinates tool under Download tool group.
- If using the Define Download Area by Coordinates, a dialog will appear that is used to define an area for download.
- Once the area is defined you will be taken to the download page. You will need to click "Modify Data Request" and change the format to the BIL_16INT format. Click "Save Changes & Return to Summary".
- Click "Download". You will be prompted to save the file once it is ready for download
How to use the seamless NED and SRTM data with the Pathloss program.
Decompress the dataset to its own directory. The dataset is comprised of 10 files…
| *.BIL | METADATA.DBF |
| *.BLW | METADATA.PRJ |
| *.HDR | METADATA.SHP |
| *.PRJ | METADATA.SHX |
| *.STX | METADATA.TEX |
In Version 4.0 make sure to use NED CONUS for data in Alaska. Do not use NED Alaska.
The NED (CONUS) data uses the NAD83. NAD27 Coordinates are transformed automatically.
The SRTM data uses the WGS84. NAD83 and NAD27 Coordinates are transformed automatically.
In the Pathloss program click Configure – Terrain Database and depending on the dataset select either NED CONUS, NED Alaska or SRTM from the drop down list.
Click Setup Primary (or Secondary depending on your selection).
Click the file button and browse to find and load the file with the BIL extension. The program is now setup to use the selected BIL file.
