Display Manager organizes the data in your map into layers, which you can display and style independently. Each layer contains one type of data. For example, you might have a layer of drawing objects, a layer that represents a feature class from Oracle, a DEM surface layer, and a raster image layer. When you use to connect to a data source (via Data Connect), each feature class or image in that data source becomes a separate layer automatically. You can create drawing layers for drawing objects, and these objects can be members of multiple layers.
If an object is a member of more than one layer, it inherits the style of each layer of which it is a member. For example, if a line is in both the Transportation layer and the Roads layer, it inherits the styles of both layers. If the layers specify conflicting style or visibility settings, the object uses the style and visibility settings of whichever layer is higher in the Display Manager list.
You can specify a thumbnail icon for drawing layers, which is used in Display Manager and in any legends you create for this map. This affects drawing layers only, and is not available for feature layers.