What is the gravity model in urban geography and how is it used in planning?

• A. It predicts weather patterns affecting urban areas.
• B. It determines zoning boundaries only.
• C. Interaction between places based on their size and distance; used to forecast commuting flows, retail catchments, and service areas.
• D. It assesses soil quality in urban perimeters.

Answer: (C)

The gravity model focuses on how places interact based on their size and their distance from each other. In urban geography, larger places generate more potential interaction (more people, more services, more jobs), while interactions decrease as distance between places grows. This simple idea mirrors gravity: attraction grows with mass and weakens with distance.

In planning, this model is used to forecast flows such as commuting between home and work, trips for shopping, and movements to services like hospitals or libraries. It helps planners estimate where people are likely to travel from and how strong those flows will be, which in turn informs decisions about transportation needs, locating new facilities, and defining retail catchments or service areas. A typical use is to predict how many residents of one area will travel to a given center, or how much demand a new supermarket might attract from surrounding neighborhoods.

So the best description is that interaction between places depends on their size and distance, and it’s used to forecast commuting, retail catchments, and service areas. The other options describe weather patterns, zoning boundaries, or soil quality, which are not what the gravity model measures.