The central business district (CBD) is where a large amount of businesses are located. In the concentric zone model, it is located in the center of the city. Houses and apartments are less common in the CBD and tend to be more prevalent outside of it.

The outermost zone of the concentric zone model is the commuter zone, which includes the suburbs. These are the people who live furthest away from the central business district and therefore have to commute the greatest distance to work.

 The factory/industry zone is the blue on the left, and it is located surrounded by the low class residential zone (green) and touching the central business district (red).

A city that lacks a centralized business district or downtown area and that has several distinct neighborhoods that all act as regional centers within one larger city is best captured using the “Multiple-Nuclei Model.”

A Multiple-Nuclei Model city is a city that does not have one central area, but instead has several nodes that act as regional centers for economic or residential activity within one larger city. Los Angeles, with its many distinct neighborhoods, is a prototypical example of this type of city.

Lagos is the capital city of Nigeria and is by far the most populous city in Africa. More than ten million people live within the city of Lagos, and an additional ten million live within the metropolitan area of Lagos. The next most populous cities in Africa are Cairo, in Egypt, and Kinshasa, in the Democratic Republic of Congo.

A “gateway city” is a city that serves as a port of entrance for migrants arriving in a country or a large geographic region. Cities like New York City, San Francisco, and Rio de Janeiro are classic examples of gateway cities.

In human geography the term “gateway city” refers to a city that acts as a port of entry into a country or a large geographic region. San Francisco with its natural harbor and immigrant population, often referred to as the “gateway to the west,” is a classic example of a gateway city.

Medina is a prominent city in Saudi Arabia and, with its mosques, open-air markets, and prominent courtyards. As such, Medina is a classic example of an “Islamic city” from religious, cultural, and aesthetic perspectives. Sofia is in Bulgaria; Venice is in Italy; Barcelona is in Spain; Tblisi is in Georgia.

London, Tokyo, and New York City are the only cities in the world that are considered to be first-tier world cities. This means they are global centers of culture, economics, and politics that have a disproportionately massive influence on the global population. Capital cities and economic centers like Moscow, Brussels, Mumbai, Los Angeles, and many others are considered to be “second-tier world cities.”