The Gravity Model is based on Isaac Newton’s law of gravitation. It is a mathematical formula, so it cannot rely on something like “cultural output” because this is unquantifiable. It instead relies on population size and distance. The Gravity Model holds that the interaction between two places can be determined by the product of the population of both places, divided by the square of their distance from one another. The primary implication of this model is that distance is not the only determining factor in the interaction between two cities. For example, although Kingston, Canada is much closer to New York City than London it also has a much lower population than London so the interaction between London and New York City is likely to be higher than the interaction between Kingston and New York City.

The rank size rule states that the  largest city in a given country will have  of the population of the largest city in that country. If the largest city has a population 1,000,000, and we want to know the population of the fourth largest city, it will have  of the population of the largest city.  of 1,000,000 is 250,000 people.

The “rank-size rule” is related to the relative size of cities. According to the rank-size rule, there should be a larger number of small cities than bigger cities. Also, this rule predicts that the larger a city’s population is then the fewer number of cities there should be in the surrounding area with a similar population.

Mexico's population distribution is an example of a primate city. Mexico City has a population that is more than double the population of Guadalajara, therefore not qualifying the population to be under a rank-size rule. Cities can be world cities, alpha cities, or capital cities and not have the population disparities found in countries like Mexico.

The term “primate city” is used to refer to a city that functions as by far the largest city in the country it inhabits. It may have a population between a third and a half of that of the whole country. Classic examples of primate cities include Bangkok in Thailand and Seoul in South Korea.

A “primate city” is a city that serves as by far the biggest city in the country that it inhabits. It’s population is exponentially greater than the population of the next largest city in that country. These types of cities typically arise in “postcolonial” settings because during the colonial era it was common for the European governments to carry out all their political and economic activity through one regional center. This led to infrastructure being disproportionately developed in one centralized area. After decolonization this infrastructure remained in place.

By definition, mercantile refers to anything of or relating to trade. A mercantile city is a trade city which developed because of the trade routes. Most of these cities benefit from being on the coast because they can have a port, but after train transportation became prominent, having a port was no longer an essential element to being a mercantile city.

The “central place theory” states that in any given region there can only be one large central city, which is surrounded by a series of smaller cities, towns, and hamlets. The central city provides goods and services that meet the needs of the people living in the smaller communities; furthermore, the people living in the smaller communities provide part of the labor supply and market required by the city.

The “central place theory” was developed in the 1930s by Walter Christaller. According to the “central place theory” in any given region there can only be one large central city which is surrounded by a series of smaller cities, towns, and hamlets. The central city provides the goods and services required by people living in surrounding communities. John R. Borchert is responsible for organizing American urbanization into five different epochs, called Borchert's Epochs. Johann von Thunen developed a model of modern agricultural land use. Alexander von Humboldt's work laid the foundation for biogeography.

In “central place theory” the outlying towns and small communities that rely on the central city for goods and services are known as “hinterlands.”