Apply the same colormap and numeric range to two maps

When performing qualitative comparisons of different maps, analysis is made much easier when all maps use the same colors to represent the same values. 

By default, Surfer applies the colormap for contour and color relief maps between the z minimum and z maximum values of the grid file. This makes it likely that a specific color in one map will not be associated with the same value in another map. 

The Before image above shows two slope maps using the same colormaps over different data ranges.  In this example both maps appear to have a lot of areas with extreme slopes. The After image above shows how applying the same data range can impact comparisons between the two maps. The updated example makes it clear that the map on the right has significantly more areas with severe slopes.

Change the Z values associated with your colormap

Before making any adjustments to your map you must first choose a colormap data range that will covers the Z extents for all maps you're working with.  The minimum and maximum Z values for any grid based map can be found on the Info page in the Properties window

1. Click the Contours layer in the Contents window.
2. On the Levels page in the Properties window, adjust the Minimum contour and Maximum contour, if desired.
3. Click the Custom colormap (...) button in the Fill Colors field.
4. In the Colormap Editor dialog, type the desired data minimum into the Min field, and type the desired data maximum into the Max field.
   
5. Click OK.
6. Repeat steps 1-5 for each of your other maps or use the copy/paste format feature to apply all of the same settings to both maps:
   1. With the Contour layer still selected, click Home | Clipboard | Copy Format. 
   2. Select the other Contour layer and click Home | Clipboard | Paste Format. 

Note: This same process can be applied to color relief maps.  The primary differences are that the minimum and maximum contour cannot be adjusted and the Custom colormap button is found on the General page of the Properties window.