Scale can be made immediately apparent by the use of human figures proportional to the model. The plan for the redevelopment of downtown Philadelphia, Pa., was aided by a model showing the area as it then existed. The part representing the area under consideration could be turned over mechanically to reveal the projected improvement. Scale models of entire proposed factories are used to check location of machinery, stock rooms, loading docks, offices, and other features and to determine the efficiency of production-line assembly. The early stages of the design of nearly all manufactured products require the construction of small-scale models.
Models are especially valuable in the field of aerodynamics.
A model of an aircraft is tested in a wind tunnel that simulates speeds exceeding those of sound. Industry has its own educational programs and uses cutaway or clear plastic models to demonstrate working relationships of machine parts and problems of assembly and disassembly. It is here that oversize models are often used to demonstrate the functioning of small mechanical parts. Magnified parts are also used by watchmakers and other manufacturers of tiny, intricate components. Large models of geographic regions have been constructed to study water flow.