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Urban Heirarchy is a term that relates to the structure of towns within an area. It can typically be illustrated by dividing towns into 4 categories:

- 1st Order Towns

- 2nd Order Towns

- 3rd Order Towns

- 4th Order Towns

1st Order Towns provide the bare minimum of essential services, such as bread and milk. The services which 1st Order Towns provide require only a very low threshold population to survive, which make them suited to small communities. Services which require more customers to remain viable are not found in 1st Order Towns.

3rd and 4th Order Towns are larger cities and communities. They are home to services which people aare willing to travel longer distances to get to, as they are more important or rarer. The services in 3rd and 4th Order Towns require large threshold populations to survive, which is why they are only found in more developed areas.

It is clear to understand, therefore, that there should be more 1st Order Towns than 4th Order Towns, as 1st Order Towns only require a small amount of people in their Hinterland to remain viable.

A German Geographer named Christaller also proposed the concept of the K-Ratio to describe the amount of towns in one order in relation to the next. While Christaller's model is rarely found, it still provides a useful rule for the establishemnt of towns.

If a country had a K-Ratio of 3, for example, this would mean that there would be 3 times as many towns in the order beneath the current one. For example, if a country had the following amount of towns in the relevant orders:

1st Order Towns = 27

2nd Order Towns = 9

3rd Order Towns = 3

4th Order Towns = 1

The country or area would be said to have a K-Ratio of 3, as a large, 4th Order Town had 3 3rd Order towns within its hinterland, 9 2nd Order Towns and 27 1st Order Towns.