Best Plane UV mapping creates UVs for a polygon mesh based on the faces / vertices you specify by projecting the best possible plane connecting components you specify. It's especially useful for projecting onto a subset of selected faces.
		
 
	 To map UVs using a Best Plane mapping
- Select faces on the object you wish to create UVs for (or the entire object itself). 
		
- Select 
		  . 
		  Maya automatically switches to component mode. 
		   
- Shift + select at least one face, or 3 vertices/CVs/locators to define the projection plane. 
		
- Press Enter. 
		
Maya maps the UVs to fit a plane encompassing the selected components.