American Institute of Certified Planners (AICP) Practice Exam

According to the Retail Gravitational Law, the trade attraction from two cities is related to what factor?

1. Distance from other towns

2. The square of the distances from the two cities

3. The total land area of the cities

4. The local economy size

The correct answer is: The square of the distances from the two cities

The Retail Gravitational Law posits that the trade attraction between two cities is inversely proportional to the square of the distance separating them. This concept is derived from the gravitational model used in physics, where larger distances result in weaker attractions. The rationale is that as the distance between the two locations increases, the likelihood of patrons traveling between them diminishes, significantly affecting the trade volumes. Hence, the square of the distance reflects not just the linear impact of distance but also emphasizes the diminishing returns on trade attraction as distance grows. This modeling approach helps urban planners and retailers to understand trade areas and competition dynamics effectively. In contrast, the other factors—such as distance from other towns, total land area, or local economy size—do not capture the underlying relationship described by the Retail Gravitational Law as clearly as the square of the distances does. While those aspects may influence trade and economic interactions, they are not the primary consideration according to the established principles of the Retail Gravitational Law.