Technical Drawings - sometimes also called "working drawings" - are a significant part of a set or lighting design. A sketch or rendering communicates information about the appearance of an object, but little or no information about its exact size. That information is essential if an object is to be built or assembled. Precise graphic information about size, proportion, and structure is essential in architecture and engineering, and the art and science of technical drawing was developed over many centuries in these fields. The process of making technical drawings is frequently called "drafting."

Representational drawing and sketching is concerned with "drawing what you see," or "drawing that which you imagine as if you actually saw it." Technical drawing is concerned with representing objects according to conventions that allow size, proportions, and structure - as well as appearance - to be precisely specified. The most fundamental concept involved is the geometry of "projection."

This process uses principles of orthographic ("true drawing") projection. It also works in reverse: if you correctly draw the individual views onto the pieces of glass, fold them all up into a box with 90 degree corners, then project points from each drawing into the middle of the box, the resulting intersections will define the 3 dimensional object.

The advantage of this process is that it's possible to apply a uniform system of co-ordinates (a "measurement grid") to the pictures created in each view, and it's possible to apply proportion ratios to these drawings - to "scale" them. It isn't usually practical to make a drawing "actual size" - most objects are larger than most pieces of paper. But if we use a standard unit of measure, and then reduce the size of the drawing by a standard ratio, we can specify exact proportions and measurements on a drawing that is much smaller than the real thing. So: on a technical drawing using the metric measure, scaled in a proportion of 1:10, 1 mm will equate to 10 mm actual size. On a technical drawing using the imperial measure, scaled in a proportion of 1:24, 1/2 inch will equate to 12 inches actual size.

There are a number of other systems of projection geometry in addition to the orthographic one: central (or perspective) projection, oblique projection, etc. In Scenery and Lighting Design, the expected technical drawings normally use the conventions of orthographic projection in order to specify the size, proportions, position, and spatial relationships of the objects designed.