Detailed Drawings > Controlling Drawing Details with Layers > About Utilizing Default Layers in Drawings
  
About Utilizing Default Layers in Drawings
You can automatically place specific drawing item types on a layer by defining a default layer. You can use the def_layer configuration option to define which drawing item type to automatically place on a layer. When you create or show a drawing item type, it is simultaneously placed on the layer.
For example, if you use the layer_dim_<layer name> configuration option and create or show a dimension, it is automatically placed on the designated layer. You can either define a default layer that contains only one drawing item type, such as dimensions, or you can place all drawing item types on a particular layer.
You can also activate a layer to control the placement of drawing items on that layer. Though multiple layers can exist in a drawing, only one layer is active at a time.
You must manually activate and deactivate an existing or a created layer.
A default layer is activated automatically if you create it using the def_layer configuration option. Otherwise, you must manually activate it. If you manually create the layer (Layer > New Layer), you must manually activate it.
If a drawing has one model or multiple models, drawing item types are placed on the layer for the reference model. For example, if you create a geometric tolerance in a drawing that uses a part as its model reference, the geometric tolerance is stored in the active layer of the part.
 
Items shown for the first time are added to the active layer. However, if a shown item was previously erased or removed from the layer, it is not added to the layer.
You cannot activate ruled layers.
You can use default layer models to generate ruled layers in parts the same way the def_layer configuration option works. This allows more complex ruled layers to be automatically created in models when needed.