How do I make all Z values above (or below) a certain threshold value transparent in Surfer?

You can tell Surfer to only fill areas in a map where the Z is above or below a certain threshold value. How you do this depends on the type of map you have.


Let's say you want to color only the areas of the map where the Z value is less than 150 (so all areas where Z is greater than 150 are transparent). You could do this a few different ways.


If you have a map:

  • If you are using a contour map, then simply set the contour maximum value to the value you want. For example:
    1. Select the Contour layer in the Contents window.
    2. In the Properties window on the Levels page, set the Maximum Contour to 150. No contours above that will be drawn.
    3. To eliminate the fill if the contours are filled, either:
      • Change the Level method to Advanced, click Edit Levels, double click the Fill for the last layer, change the Opacity to 0%, and click OK twice. 


      • Click the Custom colormap (...) button to the right of Fill colors to open the Colormap dialog. 
        1. In the Colormap dialog:
          1. In the Data to Color Mapping section, set the Maximum to 150.
          2. Select the last node.
          3. Uncheck the box next to Apply opacity to ALL nodes, then decrease the Opacity to 0%.
          4. Click OK and the new color map is applied.
  • If you have a color relief map, then you would do this in the Colormap dialog as well:
    1. Select the Color relief layer.
    2. In the Properties window on the General page, click the Custom colormap (...) button to the right of Colors to open the Colormap dialog.
    3. Perform step 3a above.

If you want to edit the grid to remove the nodes above that cutoff value:

  1. Click Grids | Calculate | Math.
  2. In the Grid Math dialog, click the Add Grids button, select the grid file and click Open.
  3. Enter the function: IF (A>=150, 1.70141e+38, A). This tells Surfer that if the Z value in the grid is greater than or equal to 150, then convert it to the Surfer NoData (1.70141e+38), otherwise leave the grid value alone.
  4. Enter a new Output Grid name and click OK to generate the new grid.
  5. Create the map from the new grid.


Updated September 12, 2017


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