ABSTRACT
Many of the operational urban models that have been developed are based on the concept of the gravity model. It is referred to as the gravity model because of its analogy with the physical and conceptual ideas of Newton's law of universal gravitation in physics. Using Newton's gravity principles, Reilly proposed two simple rules that would help to describe the flow of retail trade between towns and cities. The breaking point between two cities is defined as a point to which one city exercises the dominating retail trade influence, and beyond which the other city dominates. Reilly carried out extensive empirical work to demonstrate that the 'law' actually worked. He studied the breaking point between large cities all over the USA and in each case the field study result was very close to that obtained by applying the law of retail gravitation.
