Gridding with Breaklines in Surfer

Breaklines are used to define boundaries or geologic features with known Z values. For example, a breakline can be used to define the bank of a creek, river, or lake. Surfer requires breaklines and faults to be defined in a BLN file. If the BLN file is not being recognized or used as expected, there are a few things you can check.


Example of a BLN file in Surfer's worksheet

Example of a polygon in BLN format with a blanking value of 1.


BLN formatting:

  1. Click File | Open in worksheet.
  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 X, Y, and Z 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. Reshape the objects manually:
      1. Click on the Base layer in the Contents window.
      2. Use the Reshape and any other necessary commands from this Features tab to correct the issue.
    2. Edit the coordinates in the Properties window:
      1. Expand the Base layer in the Contents window and select the desired object.
      2. Click the Coordinates tab in the Properties window. The coordinates of each vertex are listed in order from left to right
      3. Click on the desired coordinate and enter the correct value.
    3. Turn off the axes by unchecking them in the Contents window.
    4. Click File | Export.
    5. Give your file a name, change the Save as type to BLN Golden Software Blanking (*.bln), and click Save.
    6. Click OK in the Export Options dialog and the new BLN file is created.


Once the BLN file contains the correct breakline objects, the data can be gridded by completing the steps below.

  1. Click Home | Grid Data | Grid Data.
  2. In the Select Data page of the Grid Data dialog, click Browse.
  3. In the Open Data dialog, select the data file and click Open
  4. Select the Gridding Method and assign the X, Y , and Z columns in the Grid Data dialog. 
  5. Click Next to view the Kriging - Variogram page, if using the Kriging gridding method.
  6. Click Next to view the Options page.
  7. Expand the Breaklines and Faults section (this may just say Breaklines or Faults depending on the gridding method used). 
    Note: In Surfer 15 and previous, click the Breaklines and Faults tab. 
  8. Click on the Open File button to the right of the File Containing Breaklines field, specify the BLN file, and click Open.
  9. Click Skip to End to view the Output page.
  10. Adjust the remaining gridding parameters as desired and click Finish to create the grid file.


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 screen shots of your gridding parameters to




Updated November 2021

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