A drawing composed of other compound or simple drawings.
Eventually all drawings should resolve to elementary shapes but the hierarchy can be arbitrarily deep. Each component is scaled and positioned relative to its parent.
The main use of drawings in Catacomb 2 is to allow replacement of the visual representation of a compound object by something simpler. By default a compound object will be drawn by drawing all its subcomponents scaled down and proceeding down the hierarchy until it gets to elementary components.
For complex components this is both slow and not very useful since the individual items get too small. It can, therefore, be useful to replace the default representation of a compound object with a new drawing acting as a mnemonic for the function of the compound.