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To use SDTS DEM data from the USGS in Surfer:

In Surfer 8, 9 and 10, you can use the new format USGS SDTS Digital Elevation Model files [.DDF] in any place a grid file is required: 

1. Download SDTS DEM data*
1. The Geo Community
2. USGS Geographic Data Download
   
   
2. Unzip the data using a program like WinZip or similar
1. Note:  If you are using WinZip - Go to Options | Configuration, Miscellaneous tab and in the Other category, un-check 'TAR file smart CR/LF conversion' in order to properly unzip the files.
2. When you unzip the file (for example, 3809474.DEM.SDTS.TAR), there will be many [.DDF] files that are contained in the SDTS transfer. All these files must be together in the same folder.
   
   
3. In Surfer, select a command that prompts you for a grid file (ie. Map | New | Contour Map).

1. Download SDTS DEM data*
1. The Geo Community
2. USGS Geographic Data Download
   
   
2. Unzip the data using a program like WinZip or similar
1. Note:  If you are using WinZip - Go to Options | Configuration, Miscellaneous tab and in the Other category, un-check 'TAR file smart CR/LF conversion' in order to properly unzip the files.
2. When you unzip the file (for example, 3809474.DEM.SDTS.TAR), there will be many [.DDF] files that are contained in the SDTS transfer. All these files must be together in the same folder.
3. The .DDF files will have the same name structure
1. Four character prefix (ex: 3809), same prefix for each file
2. Four character identifier (ex: CATD, CATS)
3. Three character extension [.DDF] 

3. Convert the DDF files to one DEM file using a freeware SDTS2DEM*
1. Download the sdts2dem.exe program from: http://data.geocomm.com/dem/sdts2dem.html 
2. Place a copy of sdts2dem.exe in the folder containing the unpacked .DDF files.
3. Double-click on sdts2dem.exe. You will be prompted for 3 responses:

                    i.  DDFbase: Enter the first 4 characters (4 numbers will be the same for all DDF files) in the prefix of the SDTS DDF file and hit the Enter key.

                    ii.  DEMbase: Enter an output DEM file name of your choice (up to 8 characters, no spaces or symbols) and hit the Enter key.  You can change the name after the DEM file is created.

                    iii.  Cell_id: Enter the characters in the position 7 and 8 of CELL file name (usually l0, lowercase L and number 0) and hit the Enter key.

4. After the DEM file is created, the window will automatically close and you can delete the DDF files from the STDS compressed file.  You may want to keep the STDS TAR. GZ file in case something happens to your DEM file and you need to create a new one.

5.  In the Open dialog, select a DEM file and click Open.

Some additional reading*

• USGS, What is SDTS? http://mcmcweb.er.usgs.gov/sdts/whatsdts.html
• USGS, SDTS FAQs: http://mcmcweb.er.usgs.gov/sdts/sdtsfaq.html

 
*Golden Software is not affiliated with and does not support any links for downloadable data.  Users may follow the link and download data at their own risk.  The links are simply examples of locations that offer free data downloads, and we bear no responsibility for downloads from GeoComm or the USGS.