The gravity model is a popular mathematical model used to predict the interaction between two or more places. In geography it has been used to simulate a variety of flow patterns, such as traffic and mail flows, telephone calls, and migration. Essentially, the gravity model can be used to account for any interaction or flow that is expected to move from one place to another. This idea has generated many mathematical manipulations of the model.

The original gravity model is based on Newton's law of gravitation, expressed as

where Gij is the gravitational bond between objects i and j, G is the gravitational constant, Mi and Mj are measures of the attractiveness of masses i and j, and d2ij the square of the distance between objects i ...