Which model predicts spatial interaction between places based on the product of their populations divided by the distance separating them?

Which model predicts spatial interaction between places based on the product of their populations divided by the distance separating them?

• A. Gravity Model
• B. Central Place Theory
• C. Rostow's Stages of Growth
• D. Demographic Transition Model

Answer: (A)

The gravity model explains spatial interaction between places by linking it to how big the places are and how far apart they are. It borrows from the idea that places with larger populations have greater pull, and that distance between places dampens interaction—the farther apart two places are, the less interaction they have. The key formulation uses the product of the two populations in the numerator, reflecting that interactions grow with the size of both places, and distance in the denominator, reflecting the friction or cost of moving goods, people, or information. This setup captures why a large city and a nearby town might exchange far more goods and people than two small towns far apart, even if their needs or opportunities are similar. In AP Human Geography, this model is used to estimate flows like trade, commuting, or migration, with the distance term sometimes raised to a power to better fit observed data. The other listed theories focus on different ideas—Central Place Theory maps how settlements organize services in a patterned lattice, Rostow’s Stages of Growth describes development stages, and the Demographic Transition Model tracks changes in birth and death rates over development—none of which specifically model spatial interaction through the product of populations divided by distance.

The gravity model explains spatial interaction between places by linking it to how big the places are and how far apart they are. It borrows from the idea that places with larger populations have greater pull, and that distance between places dampens interaction—the farther apart two places are, the less interaction they have. The key formulation uses the product of the two populations in the numerator, reflecting that interactions grow with the size of both places, and distance in the denominator, reflecting the friction or cost of moving goods, people, or information. This setup captures why a large city and a nearby town might exchange far more goods and people than two small towns far apart, even if their needs or opportunities are similar.

In AP Human Geography, this model is used to estimate flows like trade, commuting, or migration, with the distance term sometimes raised to a power to better fit observed data. The other listed theories focus on different ideas—Central Place Theory maps how settlements organize services in a patterned lattice, Rostow’s Stages of Growth describes development stages, and the Demographic Transition Model tracks changes in birth and death rates over development—none of which specifically model spatial interaction through the product of populations divided by distance.