Here is the procedure that I used to build the landscape in Blender.
1) Go to seamless.usgs.gov.
2) Click view and download US data. I have not had much luck with the international elevation data.
3) The zoom tool is highlighted. Drag a box around the area of the US you are interested in. The screen refreshes.
4) Keep zooming in with the procedure in 3) until you see the area you are interested in.
5) Under downloads, Click on the Define Rectangular Download Area button.
6) Drag a box around the area you want to download. Do not make the box too big. An area the size of a mountain is good.
7) A new page will open (National Map Seamless Server Request Summary Page).
8) Click modify Data request.
9) Scroll down to the box checked National Elevation data (NED). Change ArcGrid to Geotiff with the pull down menu button.
10) Scroll to the bottom of the page, and click Save changes and Return to summary.
11) Click Download.
12) Save the zipped file to disk (It will end up on your desktop).
13) Right click on the file on the desktop and extract to a new file on your hard drive. Click next and finish.
14) You now have elevation data, but it is not easy to open.
Making a height mapI use Esri's Arcview software with the spatial and 3d analyst, but this software is expensive. I found a freeware program called 3DEM that also works. You can download it for free from
http://www.visualizationsoftware.com/3dem.
15) Install the 3dem software and run it. Select GeoTiff Dem and click ok.
16) Navigate to the folder with the GeoTiff file that you downloaded from the USGS seamless server.
17) Select Geocoordinates, lat-long Grid off.
18) Move the Box off the map.
19) Get rid of hill shading. Click Colorscale shaded relief. Set Shade depth from 100 to 0. Click ok.
20) Set Color Scale to a Grey scale. Click color scale, Modify scale. The color for the lowest elevation is selected. Slide each of the RGB sliders to zero. Then click on the next elevation, and move the sliders to 18, Click the next elevation, and move the sliders to 36. Continue up the elevations increasing the sliders by 18. You should save this file, so you do not have to do this again.
21. Click file, save map image. Click jpeg or bmp. You now have an exact height map that you can import into blender to create a landscape. Follow the procedure: Create Grid and add the image as texture in the from Noob to pro tutorial to generate the landscape.