Chapter 6 Using Layers to Organize Your Drawing Before the age of computers, drafters used sets of transparent overlays on their drafting tables. These overlays were sheets that stacked one on top of the other, and the drafters could see through several at a time. Specific kinds of information were drawn on each overlay. All of them related spatially so that several overlays might be drawn for the same floor plan. Drawings for each dis- cipline, such as plumbing, electrical, or HVAC, as well as charts and tables, were drawn on separate overlays so that the floor plans did not have to be replicated for every type of drawing produced. Each overlay had small holes punched near