Model is a day-to-day word. Look it up in the dictionary so you are likely to find for upwards of eight definitions as a noun and four or more as a verb. Meanings vary from making things out of clay to using mathematics to somebody that struts down the catwalk. Leaving aside this last category, most of the definitions have a very important factor in common: simplification or reduction in complexity. At its easiest, a model is a simplification of reality in terms that we can easily understand. As illustrated in Figure 4.1, a map can be viewed as a model.