In urban studies, urban primacy indicates the ratio of the largest city to the next largest i.e the second largest in a country. Such a city is called a primate city. In other words, urban primacy can be defined as the central place in an urban or city network that has acquired or obtained a great level of dominance. The level of dominance is measured by population density and the number of functions offered. Higher functions and population will result in higher dominance.
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Urban primacy Wikipedia(Text) CC BY-SA