Central place theory

Central place theory is a geographical theory that seeks to explain the number, size and location of human settlements in an urban system. The theory was created by the German geographer Walter Christaller, who asserted that settlements simply functioned as 'central places' providing services to surrounding areas.

To develop the theory, Christaller made the following simplifying assumptions:

All areas have:

Therefore, the trade areas of these central places who provide a particular good or service must all be of equal size

The theory then relied on two concepts: threshold and range.

The result of these consumer preferences is that a system of centers of various sizes will emerge. Each center will supply particular types of goods forming levels of hierarchy. In the functional hierarchies, generalizations can be made regarding the spacing, size and function of settlements.

The higher the order of the goods and services (more durable, valuable and variable), the larger the range of the goods and services, the longer the distance people are willing to travel to acquire them.

At the base of the hierarchy pyramid are shopping centres, newsagents etc. which sell low order goods. These centres are small. At the top of the pyramid are centres selling high order goods. These centres are large. Examples for low order goods and services are: newspaper stalls, groceries, bakeries and post offices. Examples for high order goods and services include jewelry, large shopping malls and arcades. They are supported by a much larger threshold population and demand.

From this he deduced that settlements would tend to form in a triangular/hexagonal lattice, this being the most efficient pattern to serve areas without any overlap.

In the orderly arrangement of an urban hierarchy, seven different principal orders of settlement have been identified by Christaller, providing different groups of goods and services. Settlement are regularly spaced - equidistant spacing between same order centers, with larger centers farther apart than smaller centers. Settlements have hexagonal market areas, and are most efficient in number and functions.

The different layouts predicted by Christaller have K-values which show how much the Sphere of Influence of the central places takes in — the central place itself counts as 1 and each portion of a satellite counts as its portion:

According to the marketing principle K = 3, the market area of a higher-order place(node) occupies 1/3rd of the market area of each of the consecutive lower size place(node) which lies on its neighbor; the lower size nodes(6 in numbers and 2nd larger circles) are located at the corner of a largest hexagon around the high-order settlement. Each high-order settlement gets 1/3rd of each satellite settlement (which are 6 in total), thus K = 1 + 6×1/3 = 3.

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