Central place theory explains why big cities are few and small towns are many

Those two limits sort settlements into a spaced hierarchy.

Threshold and range set what a place can sell

A central place is any settlement that supplies goods and services to the area around it, its market area or hinterland. The threshold is the minimum number of customers needed to keep a business open. The range is the maximum distance people will travel to buy something. A bakery has a low threshold and a short range, so it appears even in villages. A specialist hospital needs a huge population and draws patients from far away, so only a large city can support one.

Low order and high order goods build the hierarchy

Goods that people buy often and cheaply, such as bread, gasoline and haircuts, are low order goods. Goods bought rarely, such as furniture, designer clothes or concert tickets, are high order goods. Every place that offers a high order good also offers the low order ones, so the system nests. The result is an urban hierarchy: many hamlets and villages, fewer towns, a handful of cities and one or two regional capitals at the top, each level spaced farther apart than the one below.

Why the market areas are hexagons

Walter Christaller assumed a flat plain with even soil, evenly spread customers and equal travel in every direction, with each shopper buying at the nearest place. Under those conditions each market area would be a circle. Circles either overlap or leave gaps, though, and a gap would mean customers nobody serves. Hexagons tile the plain completely while staying close to a circle, so Christaller drew the market areas as hexagons, with small ones nested inside larger ones. August Losch refined the pattern in 1940.

Central place theory versus the rank size rule

Students often blend this model with the rank size rule because both appear in Topic 6.4. The rank size rule is a statistical description: it predicts a city's population from its rank. Central place theory explains spacing and function. It says why a regional city sits a certain distance from its neighbors and what it offers that a town cannot. A question about how far apart places are, or why a service is missing, points to Christaller.

Where the model fails and the common exam slip

Real regions break the assumptions. Rivers, mountains and highways bend market areas, and population is never spread evenly. Cars stretch the range of almost every good, and online shopping weakens the link between buying and distance, a change best explained through friction of distance. The classic slip is swapping the two terms. Threshold counts people, range measures distance. An answer saying a town lacks a hospital because its range is too short names the wrong limit.

Using the model on a free response question

A typical prompt describes a small town that lost its department store, or a rural county with no specialist doctor, then asks you to explain the pattern. Name the good's order, state that the local population falls below its threshold, and say that residents now travel to a higher order place within the good's range. Revise with your own diagram: photo to quiz turns a sketch of nested hexagons into questions, and the Unit 6 page links the other city models.

Last updated: 2026-10-03 · Written with AI assistance and reviewed before publishing.