The lighting for the house is mostly controlled by Insteon (SmartHome) switches and keypads. These are capable of controlling each other and being controlled by a separate software application (that doesn't exist as of this writing). To keep walls from being cluttered, most switch locations only have a single Keypad, even if the room actually has multiple lighting circuits. The keypad controls one of the circuits and the other circuits are controlled by switches located in a separate location - either the upstairs hallway or downstairs wiring closet.
Each circuit is assigned an identifier that shows up on the lighting plans and in a spreadsheet that documents all the lighting and electrical circuits (as well as much of the low-voltage wiring).