A mask is a bitmap or polygon layer that identifies specific areas to edit. You can apply various operations to update the values of the digital elevation model (DEM) covered by the mask. Masks are stored on a separate mask layer that can be saved for future editing. In the DEM Editing window, you can work with polygon (vector) or bitmap masks.
To edit DEMs produced from airphotos in which considerable cleanup is required, such as, flattening lakes, adding and removing buildings, bridges, and so on, you can use polygon masks.
To edit a DEM using a polygon mask
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In the DEM Editing window, click the Edit via Polygons tab.
The tab displays all of the options available to work with vector masks.
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To perform editing tasks, use the Edit via Polygons toolbar buttons.
Button Name Description 
Selection Tools Select a vector shape. 
New Shapes Click the arrow to select one of three modes in which to edit the polygon layer. There are three modes as follows:
Polygon: Select to create new polygon masks that define the area to filter 
Break Line: Select to put the polygon layer in editing mode, in which you can draw a break line that interacts with filtering. 
Stabilization Point: Select to put the polygon layer in editing mode, in which you can place stabilization points that interact with filtering. For more information about the Break Line and Stabilization Points tools, see Using break lines and stabilization points.
Vector Editing Toolbar Display the Focus vector-editing toolbar, which you can use to modify polygon masks. 
Create Polygon Layer Create a new polygon mask layer. 
Open Polygon Layer Open an existing polyon mask layer. 
Save Polygon Layer Save the polygon layer for future editing.