The base of a 3D surface in Surfer is drawn to the minimum Z value of the grid file. To adjust this, you need to adjust the minimum Z value of the grid file. To do so:

1. Right click over the 3D Surface layer in the Contents window and click Edit Grid.
2. In the Grid Editor, the lower left node is selected. That’s fine. In the toolbar, in the Z box enter the z value you wish the base to be drawn to  (e.g. -200).
3. Click Grid Editor | Options | Update Layer.
4. Click File | Close to close the Grid Editor. 
5. Click No, in the Surfer dialog asking if you want to save the changes to your grid file (you don’t want to actually change the grid file).
6. Back in the plot window, as long as the Z axis is showing automatic scaling, the base is now drawn to the new minimum Z value. 

Email surfersupport@goldensoftware.com if you would like to add your vote to our suggestion file for the ability to define a custom z value for the base to be drawn to.

See Also: How can I set the Z limits for my 3D surface map in Surfer?.

Updated October 24, 2018