If you've used landscape generator such as Bryce or Vue than you'll be familiar with this techinique. These programs use a grayscale image to generate terrain height. You can do a similar thing in Maya by coverting displacement maps into polygons. To do this you will have to assign a grayscale texture to the displacement channel of an objects shading group (NURBS or polys only). Once the displacment map is assigned, simply select Modify>Convert>Displacement to Polygons. This creates a new object that has the displaced geometry. As this is math intensive, it may take a while to compute. In the example shown, the original object was a simple NURBS plain with 16x16 U and V division. The image inset bottom left is the grayscale image that was used.

WARNING
Depending on the resolution and complexity of the grayscale image used, the resulting polygon may be a heavy mesh (see HUD inset).

Beside creating geometry that might otherwise be diffucult to model, the method saves the renderer from having to calculate the displacement and allows accurate interaction with geometry.