Spatial Distribution Analysis: General Description

Physical bodies in space are attracted to each other in proportion to their size; the force of attraction is weakened by their distance from each other. In the 1940s, the same principles were found to describe the spatial distribution of people (Stewart, 1947). The family of models based on these principles are jointly known as "gravity models."

The formulation is an elegant one. It explains a complex behavior in terms of only two variables: attraction and distance. The formula returns a measure of the attractiveness, or "pull," of one location in relation to one or more surrounding areas.

Each term of the equation makes a certain intuitive sense. Clearly, people are attracted to cities. In building her case for the importance of "eyes on the street" for safety, Jane Jacobs pointed out that people attract people; nothing is more interesting to people than other people. Similarly, shopping malls try to include a large department store (preferably two--one at each end) to "anchor" the mall and provide the "draw" that will supply customers to the smaller shops in the mall. As a result, retail activity is being drawn from the downtowns to the area around the suburban malls. Young people from small, rural towns plan to go to the city to make their name and their fortune; young people from the cities try to make it in the biggest cities, like New York ("If you can make it there, you can make it anywhere.")

The counterbalancing influence of distance is equally recognizable. Merchants recognize the "friction of distance" when they insist on having parking available within 100 ft. of their doors. Newspapers, shopping malls, and hospitals all expect to capture less of their potential market the further away the customers live. Convenience stores punctuate the landscape because people are unwilling to go very far just to pick up a quart of milk or a pack of cigarettes. The farther you are away from something, the more effort it seems to take to go there.

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