Masking Portions of a Contour Map with a Base Map

To mask areas of a contour map, you can overlay a base map or filled shape on the contour map. The base map must contain polygons that can be filled with patterns or colors that obscure the underlying contour map.

To overlay a masking base map:

  1. Create a contour map of your grid file by clicking the Home | New Map | Contour command.

  2. Select the contour map.

  3. Click the Map Tools | Add to Map | Layer | Base command and select a vector base map. This will add a base map layer to your contour map and create a single multi-layer map. Note: The base map must contain polygons (areas).

  4. Right-click on the base map in the Contents window and select Order Objects | Move to Front. The base map moves to the top of the list.

  5. When the base map is selected, the base map properties appear in the Properties window. Click on the General tab.

  6. Click the next to Fill Properties to specify the fill properties to apply to the boundaries from the base map. The map is automatically updated to show the boundaries that mask the underlying contour lines.

To add an empty base map and use the drawing tools:

  1. Create a contour map of your grid file by clicking the Home | New Map | Contour command.

  2. Select the contour map. Click the Map Tools | Add to Map | Layer | Empty Base command. This will add an empty base map on top of the contour layer.

  3. Click the Home | Insert | Polygon command to draw a polygon over the contour map. You could use any of the Draw menu commands. By drawing objects inside an empty base map, the drawn objects become map objects.

  4. When the base map is selected, the base map properties are displayed in the Properties window. Click on the General tab.

  5. Click the next to Fill Properties to specify the fill properties to apply to the boundaries from the base map. The map is automatically updated to show the boundaries that mask the underlying contour lines.

To assign the NoData value to regions of grid-based maps:

  1. Create a grid file using the Grids | New Grid | Grid Data command.

  2. Create a .BLN file. The .BLN file should have identical first and last points. This closes the polygon.

  3. Click the Grids | Edit | Assign NoData command.

    1. Select the .GRD file created in step 1 as the Input Grid.

    2. Select the .BLN file created in step 2 as the NoData Polygon Boundary.

    3. Type a File name and click OK. A new .GRD file is created.

  4. Create a contour map using the Home | New Map | Contour command. The NoData portion will not appear on the map.

See Also

Base Map

Empty Base Map

Tutorial - Assign NoData to a Grid File