He recognized that the law of gravity could be used to explain demographic phenomena by examining empirical patterns related to distance in social interactions.
When used geographically, the words 'bodies' and 'masses' are replaced by 'locations' and 'importance' respectively, where importance can be measured in terms of population numbers, gross domestic product, or other appropriate variables.
An example of this is the point at which customers find it preferable, because of distance, time and expense considerations, to travel to one center rather than the other.
A special case of gravity model is the two-step floating catchment area method (2SFCA), which is popular in health care research.
They also state that the gravity model is an unfair method of predicting movement because its biased toward historic ties and toward the largest population centers.