Gridding with Breaklines in Surfer

Q. I need technical advice on creating grids, with breaklines applied. I am creating a contour map of a creek and its banks, but I am not able to make the gridding process recognize the breakline BLN file I have created. Can you help us please?


A. To use a BLN file as a breakline for gridding, there are a few things you can check.

BLN formatting:

  1. Click File | Open.
  2. In the Open dialog, choose the BLN file and click Open. The BLN file opens in Surfer's worksheet.
  3. Verify that cell A1 contains the number of vertices (rows of data points) in the breakline. 
  4. Check to see that row 2 and subsequent rows contain XYZ coordinates in columns A, B, and C. Defining breaklines is the only workflow that requires a BLN file to have a Z value in Column C.
  5. Click File | Close to close the worksheet.


BLN contents:

  1. Click Home | New Map | Base | Base.
  2. In the Import dialog, select the BLN file and click Open.
  3. Verify that the objects in the base map layer are what you expect the breaklines to be. If there is a problem, you can either edit the file in the worksheet as specified in the previous set of steps, or you can edit the objects here by doing the following:
    1. Click on the Base layer in the Contents window.
    2. Click Features | Group | Start Editing.
    3. Use the Reshape and any other necessary commands from this Features tab to correct the issue.
    4. Click Features | Group | Stop Editing.
    5. Turn off the axes by unchecking them in the Contents window.
    6. Click File | Export.
    7. Give your file a name, change the Save as type to BLN Golden Software Blanking (*.bln), and click Save.
    8. Click OK in the Export Options dialog and the new BLN file is created.


Once the BLN file contains the correct breakline objects, you can grid the data.

  1. Click Home | Grid Data | Grid Data.
  2. In the Open Data dialog, select the data file and click Open
  3. Select the Gridding Method in the Grid Data dialog. 
  4. Click the Advanced Options button.
  5. Expand the Breaklines and Faults section (this may just say Breaklines or Faults depending on the gridding method used). 
    • In Surfer 15 and previous, click the Breaklines and Faults tab. 
  6. Click on the Change Filename button to the right of the File Containing Breaklines field, specify the BLN file, and click Open.
  7. Click OK in the Grid Data dialog to begin gridding.


If there is an issue applying the breakline to the gridding process, or you receive an error, please email the data file, the BLN file, and a screen shot of your gridding parameters to


Updated November 8, 2018

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