In Central Place Theory, what two concepts determine the size and distribution of settlements, and what is a "threshold"?

• A. Range and threshold; a threshold is the maximum service radius.
• B. Range and density; threshold is the average distance to the next town.
• C. Density and range; threshold is the minimum number of customers needed to sustain a service.
• D. Range and threshold; a threshold is the minimum number of customers needed to sustain a service.

Answer: (D)

Two ideas push how big a central place becomes and how its surrounding settlements are laid out: range and threshold. Range is how far people are willing to travel to use a service, which determines how far the service’s influence reaches. Threshold is the minimum number of customers needed to sustain that service financially—if there aren’t enough potential customers within the range, the service won’t be viable.

These ideas explain why larger settlements offer more and bigger services (they need a larger market and thus can serve people farther away), while smaller settlements host fewer, simpler services. The threshold is not about a maximum distance; it’s about the minimum market size required to make providing the service worthwhile.

Other options mix in density or define threshold incorrectly, but the essential pair is range and threshold, with threshold defined as the minimum number of customers needed to sustain a service.