ABSTRACT
Models may be classified as physical, analog, and mathematical models. The reader has probably seen physical models of buildings, dams, stadiums, theaters, or wind tunnels. These models have the same shape and appearance of the real system being studied but are generally much smaller. Analog models do not necessarily resemble the real system being studied, yet they provide important information about the system. For example, a graph showing the population increase over time is an analog model. Another example, involves the location of a new facility in an existing network of facilities.* Consider the following two examples.
