Technical drawings are created by combining multiple primitives. A wide range of drawing aids are provided to simplify the process. Placing one drawing element over another does not erase what is underneath. Color is restricted to a few dozen shades. Fills are usually solid colors or some form of cross-hatching.
File size is related to the number of drawing elements and the complexity of the drawing.
Files are stored as a database of mathematical objects. The Cartesian Coordinate system is used in both cases. Illustration Illustration software is designed to emulate the techniques used in technical illustration. Technical illustration is used to show a finished product, to show details about something that a photograph would not show, or to show a photo-realistic image of an idea or concept. These tools are somewhere between paint and CAD programs.