Most AEC Object types have a baked-in-the-program-code layer key that is used "by default" (eg, when the command is invoked from the ribbon or by typing, or when the tool palette tool selected does not have a different Layer Key set in the tool's properties. For example, Walls use the WALL layer key, Doors use the DOOR layer key, etc.
You can open up a Layer Key Style that exists in the current drawing in a number of ways. On the Manage tab, on the Style & Display panel, click the Style Manager tool. In the Style Manager dialog, you will find Layer Key Styles listed under Multi-Purpose Objects. You can open the Style Manager, filtered for Layer Key Styles, by opening the Layer Properties Manager (in 2010, the palette version, not the dialog version) and, near the top of the palette, clicking on the second icon from the left (the one with the "key" in the icon image). If you like typing, you can achieve the same filtered Style Manager result by using the LayerKeyStyle command.
If you are using the out-of-the-box AIA (256 color) Layer Key Style, you should be getting mostly layers starting with "A-" as the Discipline Designator. There are some, for site- or structural-related objects, that have "C-" or "S-" Discipline Designators. The AIA (256 color) Layer Key Style is set up to have the Discipline Designator reflect the discipline generally responsible for the design of an object type, rather than designate the discipline that is doing the actual drawing. Either approach can be used, and both are discussed in the US National CAD Standard. If you want (or need) to take the approach that anything drawn by an architect needs to have "A-" as the Discipline Designator, then you will need to edit (a copy of) the Layer Key Style to suit.
Once you have your Layer Key Style as you want it, you will probably want to save that to a central source file that all users can access, and then have everyone set that source file on the Layering tab of the Drawing Setup dialog. In 2010, you can access that dialog through the Application Menu (big red A in upper left corner) > Utilities > Drawing Setup. Set your source file as the Layer Standards/Key File to Auto-Import (use the button at the upper right, with the ellipsis [...] icon to navigate to and specify the source file). Then, in the Default Layer Standard area, set your revised Layer Key Style in the Layer Key Style dropdown list, and, finally, check the Always import Layer Key Style when first used in drawing toggle. With that checked, you do not have to worry about copying the Layer Key Style to your template files (and doing so each time you edit the Layer Key Style). Whe you open a file, the first time you use a command that makes use of a Layer Key, the program will check the source file to see if the Layer Key Style version in the source file is more recent than the one in the current file. If it is, it will automatically import the revised version into the current file.
David Koch
AutoCAD Architecture and Revit User
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