The concept describes a statistical regularity in the size distribution of cities in a region or country. It posits that the nth largest city will have a population that is 1/ n the size of the largest city. For instance, if the largest city has a population of 1 million, the second-largest city would have approximately 500,000, the third-largest approximately 333,333, and so on. This distribution creates a defined hierarchy of city sizes.
This principle is significant in understanding urban systems and predicting population distribution. A settlement hierarchy conforming to this pattern often indicates a well-integrated economic system where resources and opportunities are distributed more evenly. Historically, deviations from this rule have been used to identify regional inequalities or to point to the dominance of a primate city, which often concentrates economic and political power.