gravity model

A model of the interaction between two population centres based on Newton's Law of Universal Gravitation: two bodies in the universe attract each other in proportion to the product of their masses and inversely as the square distance between them. Thus, expected interaction between city i and city j is shown as:

k × P_i × P_jd_ij²

where P_i = the population of town i, P_j=the population of town j, d_ij=the distance between them, and k = a constant.

This original equation has been changed to accommodate features like wages, employment opportunities, and so on, and has been widely criticized, but is still used to predict future interactions. The gravity model may be applied to fields of influence of settlements, trade, traffic flows, telephone calls, and migration. Perhaps the most severe criticism of the model is that it has no theoretical basis, but is based on observation only. Furthermore, planning on the basis of the model will only reinforce differences between places; people will interact more with larger towns if planners are geared to that assumption and plan for it accordingly. see Reilly's law.

[Th]

The proposition that the degree of interaction between cultures is directly proportional to their proximity to each other.