2011

In this city map example, there are separate drawing layers for each set of
entities comprising the water system.
Use the Display Manager check boxes to turn off layers, which hides the objects
on that layer, or to turn off styles, which displays the drawing objects on that
layer without styles. For more information on styling drawing layers, see
Overview of Styling Drawing Layers (page 652).
Map Base
Objects in the current drawing that are not included in any layer are included
in the Map Base layer. You can hide all objects on this layer.
NOTE Objects from attached drawings that you have queried into the current
drawing using a standard query are added to the Map Base layer. To style these
objects separately in your map, create a query to bring them into the display.
Overview of Bringing in Drawing Data From DWG Files | 353