Object Layers Tab (Drawing Settings Dialog Box)
Use this tab to specify layers for various objects in Autodesk Civil 3D. For example, you can specify that you want all alignments on layer C-ROAD, all parcels on C-PROP, and so on. You can also specify prefixes and suffixes for the layer names.
Ambient Settings Tab (Drawing Settings Dialog Box)
Use this tab to specify default ambient (background) settings for a variety of settings, including units of measurement. These units and settings are used throughout Autodesk Civil 3D, unless they are overridden at the feature or command level.