This .NET class wraps the AcUnderlayLayer ObjectARX class. 

UnderlayLayer is an abstract class that represents underlay layers in the drawing. 

Underlays are similar to raster images but their content is snappable. An UnderlayReference must reference a compatible UnderlayDefinition. The UnderlayReference is responsible for the placement of the content within the drawing while UnderlayDefinition handles the linkage to the underlay content. 

Instances of UnderlayReference derived concrete classes are inserted in a block table record. Instances of UnderlayDefinition derived concrete classes are inserted into a dictionary of the named object.

Autodesk.AutoCAD.DatabaseServices.UnderlayLayer

Public Class UnderlayLayer
Inherits DisposableWrapper

public class UnderlayLayer : DisposableWrapper;