Borchert’s model of the development of cities tracks the growth of American cities with relation to the prevailing transportation and communication technology of different eras. The history of American cities is divided into five epochs, the five answer choices listed above. Chicago and St. Louis are two American cities that emerged in the second half of the nineteenth century as railroad hubs. Both these cities developed around the railroad and are classic examples of cities that evolved during the “steel-rail epoch.”

There are five epochs in Borchert’s model of the development of cities. The earliest is the sail-wagon epoch and the latest is the satellite-and-jet propulsion epoch. The second is the Iron Horse Epoch, and the third and fourth respectively are the Steel-Rail and the Auto-Air Amenity Epochs.

The Auto-Air-Amenity epoch runs roughly from 1920-1970. Within this epoch, the internal combustion engine transformed transportation.

Edge cities are secondary commerical centers of urban areas. Cities that have been abandoned are colloquially known as "ghost towns." The other types of cities do not have specific names, and are not considered edge cities.

In 2015, Tokyo is the world's largest metropolitan area, with a population of about 38 million people. None of the other options have more than 30 million people.

A century ago the world’s biggest cities were New York City, London, and Paris. They were the centers of the global population, however as the population of the developing world has skyrocketed in the last century so has the population of megacities in the developing world. In 2015 most of the world’s biggest cities can be found in India, China, and the African continent.

The European colonial era begins with the voyage of Columbus in 1492. At this time the capital city of the Aztec Empire, called Tenochtitlan, was by most estimates the most populous city in the world. Loose estimates, which are all that are possible, place the population of Tenochtitlan at around 200,000 people.

If the current trend continues most of the world’s most populous cities will be found in Asia, specifically South and East Asia, in the year 2025. Cities like Beijing, Shanghai, Tianjin, Delhi, Mumbai, Kolkata, Dhaka, and Guangzhou are growing at dramatic rates when compared to much of the rest of the world and will soon eclipse their western counterparts.

A “megacity” is a city that has a very large, and growing, population. Megacities are typically found in the developing world. They are characterized by high natural population growth, as well as high rates of immigration. They generally suffer from extreme pollution and poverty and will usually feature widespread slum settlements to house the working masses.

The term “megacity” is used to describe a city that has an extremely large, and growing, population. In the previous half-century megacities have been emerging all over the developing world as the population of urban environments like Mumbai, Shanghai, Lagos, and Dhaka explodes.