Remove artifacts to smooth Surfer contour maps

Gridding high numbers of data points in Surfer, especially when those data points lie along lines (like digitized contour lines), can sometimes cause irregular contour lines.
Contour map with artifacts in Surfer

You can try one of these methods to smooth the map and remove artifacts:

Option 1: Thinning out the data so there aren’t quite as many data points along the lines.

    1. To view the number of vertices along the lines, select one of the polylines and click Features | Edit Features | Reshape. That will show you all the vertices along the lines. If the vertices are so close that the boxes around the vertices run into each other, then you should thin the lines.
Reshaping contours in Surfer
The indicated polyline is in reshape mode.
The vertices are so close together, that you
cannot discern them individually.
    1. Select all the polylines in the project.
    2. Click Features | Edit Features | Thin and Smooth. You can choose any of the options. For example, select Keep Every nth Point, increase the Removal Rate, and click OK. The goal is to get the vertices spaced out a little more, so that the space between vertices is similar to the average space between the closest of the original contour lines:
Thining out vertices on contours in Surfer
Thin the polylines so that the vertices are spaced
out along the lines. In this case, 
Keep Every nth
Point was used with a Removal Rate of 30.
    1. You can select a polyline and click Features | Edit Features | Reshape again to check the spacing of the vertices. You may need to click Home | Undo | Undo and thin the lines again.
    2. If any of the lines have changed to be drastically different from the contour lines on the image, you can reshape the polyline to add or move vertices so that the new polylines conform to the original contour lines on the image.

Option 2: Changing the gridding method and/or options (e.g. including the Anisotropy value).

Option 3: Reducing the number of grid nodes in the grid file.

Option 4: Using Grids | Edit | Spline Smooth after the grid has been created to smooth the grid and remove some of the artifacts.

Option 5: Using Grids | Edit | Filter with a low-pass filter to remove background noise from the grid.

Option 6: If there are just a few areas, you can click File | Open and open the grid in the Grid Editor and modify the Z values of certain grid nodes. Save the grid and recreate the contour map.


Updated December 6, 2021

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