Developed by American astronomer James Stewart, gravity model is an examination of the interaction between two places relating to size, distance and importance. The relationship between the two places is seen as corresponding directly to product, and inversely to distance.
The gravity model is used in regional economics and transport studies. However, it is criticized for having little grounding in economic theory.
GAP Carrothers, 'A Historical Review of the Gravity and Potential Concepts of Human Interaction', Journal of the American Institute of Planners, vol. xxn (1956), 94-102