Central Place Theory

Several assumptions are vital in understanding how Central Place Theory (CPT) works:

1. Assume a homogeneous, flat plain with the same physical geography conditions (climate, soil, resources, etc.) across it. In other words, picture somewhere like Kansas or the Texas panhandle, not a mountainous region like Colorado.
2. As far as the population goes, assume that people everywhere on this plain have the same income and that, acting rationally, they will shop at the nearest market that carries what they need, and also shop at the places with lower prices for the same goods.
3. Assume that transportation costs per unit of distance are equal across the entire space.

Central Place Theory Hexagons

In the hexagons that CPT is famous for, we can see the highest-order central place, a large city (Pittsburgh, Topeka, Omaha, Amarillo, etc.), surrounded by six second-order cities (where the villager dweller goes to Walmart). A line connecting these six outlines the first-order hexagon that encloses what Christaller calls a complementary region of a higher order. Each of these six is also surrounded by six towns, outlining second-order hexagons that encompass complementary regions of a lower order.

Imagine this pattern repeating endlessly across Christaller's abstract plane/plain. This is the spatial arrangement that results from the assumptions and economic activities we described above.

Fig. 1 - This hexagon illustrates the market principle. Arrows point in the direction that economic goods and services are received

The fundamental hexagonal structure of complementary regions that CPT produces is based on Christaller's principle of market dynamics. We won't do the math here, but suffice it to say that Christaller's empirical data from across southern Germany showed that the value of goods sold in a first-order central place was much higher than that in the second-order places, which in turn was far greater than that in the third-order places. More goods and services = more people = larger city.

What about the space beyond the hexagons shown? These are complementary regions for the surrounding first-order places.

Fig. 2 - This hexagon illustrates the transport principle

The transport hexagon approximates a map of an actual transport network connecting the different places. People use roads that connect them in straight lines, the most economical way, to the places where goods and services are found. Anyone who has traveled in the US can recognize this hierarchy: the quickest routes are often the direct highways between the most significant cities, and highways reduce in size and length as they form shorter segments connecting smaller places.

Fig. 3 - This hexagon illustrates Christaller's "administrative principle"

The administrative or political-social principle recognizes that central places also have governmental functions. You may have wondered why the second-order places aren't connected to other first-order places since many people who live in them can quickly go to other first-order places to get what they need. The answer is that a central place is the center of government (in the model) for its complementary region, and all places in this hexagonal region are thus part of its administrative territory.

Translation: you will have to go to your administrative place anyway (you have no choice) for legal paperwork and other tasks involving the government, so you'll shop and take care of other business while you are there.

Central Place Theory Strengths and Weaknesses

Central Place Theory has been applied and misapplied more often than any other geographic model.

Weaknesses

As with many theories, CPT's weaknesses were recognized by its originator but ignored by those who sought to apply it too widely. The conditions that produced roughly hexagonal regions in southern Germany were vastly different than those that produced spatial settlement patterns in other parts of the world.

One common complaint is that real landscapes don't resemble Christaller's landscape. But this is because he used an abstract space; he was the first to recognize, at the beginning of his work, that the model was based on an abstraction of reality and that conditions on the ground would be different. He even recognized that mail-order businesses would skew his model; imagine what online shopping is doing to it now!

A more serious charge is the tendency to explain human settlement patterns in terms of economics and secondarily in terms of political factors, with culture a distant third—and culture itself being primarily determined by economic and political factors. It is easy to imagine a scenario of a cultural phenomenon such as ethnic tensions or differences in religion that could outweigh economic factors in determining where people went for the goods and services they needed.

Strengths

First, CPT has been enormously influential in retailing and the tertiary economic sector. Modifications of CPT are commonplace in economic models that tell retailers where to put stores, for example. Thus, based on a far more nuanced and complex CPT than we can present here, its predictive value has been one of its major redeeming features.

Second, CPT, because it became the standard for explaining spatial patterns of human settlements, inspired many variations, particularly among those who said "it doesn't fit the region I am concerned about" and proceeded to figure out a way to describe the particularities of other processes driving other patterns.

Central Place Theory Example

Photos taken by satellites at night provide some of the best visual evidence of hexagonal patterns of urban settlements on the Earth's surface.

Fig. 4 - Northwestern Europe: Paris is in the center, and London is in the lower left. Parts of France and England have a hierarchy of central places

The image in this section illustrates the hierarchy of urban sizes in Europe, particularly in the relatively physically homogeneous part of France in the lower right. CPT appears to best fit the central places in France, such as Rouen, Caen, and Le Mans, with over 100,000 people each, surrounded by second-order satellite towns, with the faintest dots being the third-order towns. Paris is a central place in its own right, the center of a hexagon comprising the entire country of France. In urban geography terms, it is the consummate primate city.