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Can I fill outside a polygon to mask the map outside a boundary in Surfer?

There is not a way to fill outside a polygon, but there are other methods to consider:

  1. To mask (or assign NoData values to) contours or any grid-based map outside a boundary, save the boundary (as a polygon) to a vector file (BLN, SHP, DXF, etc.), then use the Grids | Edit | Assign NoData command to assign null values to grid nodes that are outside the polygon. Set the header flag in the BLN file to 0 to assign NoData values outside. Create a new map with the new GRD file. 
  2. Alternatively, you can create a complex polygon that covers the area outside the boundary polygon. To do this:
    1. Load the boundary polygon as a base layer (if it is saved in a base map file format, like DXF, SHP or BLN), or add an empty base map layer and draw the boundary polygon over the map.
    2. Right click over the Base(vector) layer in the Contents window, and click Start Editing.
    3. Click Home | Insert | Polygon and draw another larger polygon outside the outer edge of all four corners of the map (so it is a rectangle that is larger than the map).
    4. Select both the large polygon you just drew and the smaller polygon defining the boundary and click Features | Islands/Lakes | Combine. This combines the two polygons into one complex polygon.
    5. Right click over the Base layer in the Contents window, and click Stop Editing.
    6. You can now fill the complex polygon with whatever fill pattern you wish. The fill will be between the boundary polygon and the larger polygon you drew.

example of a complex polygon with fill

Example of a complex polygon.

 

Updated October 20, 2017

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