Working with a Polygon Proxy
Maya 2012 Tutorial
How to Edit Subdiv Object Polygon Shape in Maya
Subdiv Surfaces are often defined by a much simpler polygon shape. As you modify the polygon shape, the organic shape of the subdiv surface follows.
Add a polygon cube to the workspace (Create > Polygon Primitives > Cube). In the cube options, set the Height Divisions to four and leave the Width and Depth divisions at one.
With your object selected, click the Component Mode icon and click the Faces icon. Delete the top face, then select the Vertices icon.
Using the Select, Move and Scale tools, reshape the object by moving and scaling groups and individual vertices.
Return to the object mode by clicking the Object Mode icon. With the object selected, choose Modify > Convert > Polygons to Subdiv.
With the Subdiv Object selected, press the 1, 2 or 3 key to display the object with greater detail. This setting only affects the preview. The final rendering is not affected.
With the object still selected choose Subdiv Surfaces > Polygon Proxy Mode in the Surfaces Menu set . You can now return to the Component Mode and reshape the polygon frame.
To return to the Subdiv Object without the polygon frame, choose Subdiv Surfaces > Standard Mode.