When creating a new drawing in Autodesk Civil 3D 2005 we must first make a decision as to how we will control the appearance of the objects, and the components, that we will be creating. The software uses two method to accomplish this.
The first method is referred to as "By Style". This method controls the appearance of an object by a style that is assigned to that object. The style sets for the object and it's components how they will appear. The layer of the object does not play a role in it's appearance. This method overrides any layer properties for the object.
The second method is referred to as "By Layer" This method assigns the components of an object to specific layers. The properties of these layers i.e. color, linetype, etc. control the appearance of the objects. This method is similar to how most AutoCAD users have traditionally controlled the appearance of objects. This method also allows for the control of the component's appearance when it is xref'ed.