What is urban growth?

Cities have been around for thousands of years. Have you thought about how cities were formed? After the Neolithic Revolution, people shifted from a nomadic lifestyle of hunting and gathering to a lifestyle of farming and settlement. Oftentimes, people gathered around water sources, such as rivers and lakes, and built non-nomadic or permanent settlements. Gradually, these settlements expanded, and small cities formed. Densely populated settlements emerged, along with the specialization and division of labor among people living in the city. Trade, bartering, or other forms of economic exchange also took place. Architecture, centralized administrations, and political structures also all became part of a city. A city is complex and encompasses all these different meanings. Two hundred years ago, the only city that had more than one million people was Beijing, China. But today, there are more than 500 cities with over a million people. This was due to the Industrial Revolution, which contributed to the development of faster means of transportation and communication methods. This ability for people, resources, and information to move around rapidly allows cities to exist.

As more cities formed, an increasing proportion of the population moved into the cities. This is called urbanization. According to statistics, in 1800, only 3% of the world’s population lived in cities. A tipping point was reached in 2008, and there were officially more people living in cities than rural areas. Urbanization has been occurring especially rapidly in less developed parts of the world. As cities and their infrastructure become more mature in developing countries, more people move into the cities from rural areas. Why would people want to move to a city? First of all, people have become less attached to land as a means of production. This means that people aren’t necessarily farmers anymore, and their jobs are not associated with farming. Therefore, moving into a city would be better for them, since cities offer a wide variety of jobs. Second of all, cities, because of the division of labor, offer all types of products and services for their residents. Thirdly, with the development of schools, people are becoming more educated or at least have better access to education. Therefore, human capital has become more important—things such as knowledge and creativity, instead of labor capital, which is based on a person being able to make money in exchange for their labor.

In the beginning, the US was largely rural. This is hard to imagine since 80% of Americans live in cities today! As we can see from the table, 3 of the top 5 growing cities are in the West, while most of the shrinking cities are in the Midwest. This potentially has to do with the shift in industries in the Midwest. New Orleans is a special case, not having recovered from Hurricane Katrina.

As cities expand, what happens in areas in between cities? Edge cities have appeared. When you are driving down the highway, you see houses, stores, and hotels located near major highway intersections. Those clusters are edge cities. Often they do not have their own mayors and belong to a bigger city or town. What about within cities, how cities change internally? One prominent phenomenon is gentrification. This is an interesting urban development pattern in the US. The middleclass move into a more under-maintained area of a city due to the increase in the number of residents and surge in rent or housing prices in expensive city centers. In doing so, the poor who primarily lived in the under-maintained areas are displaced as the middleclass drive up rent prices and buy up property. You can see this phenomenon in San Francisco and surrounding areas such as Oakland. As housing prices in San Francisco increases, middleclass residents move outwards to Oakland across the bay. As Oakland prices also increase, people look again to move outwards, further expanding into other small cities nearby. Harlem in New York City is another example. The “unsafe” image of Harlem 10 years ago is a very different one from the Harlem today full of amenities—shops, restaurants, and other services.

Another interesting city growth phenomenon in the US is suburbanization. In countries such as China, the term ‘suburbs’ is not a familiar one. This may have to do with its relatively late urbanization in the late 1980s. In the US, when inner cities become too crowded, residents started migrating to the suburbs, which are communities that are adjacent to but outside of the city. This is also called urban sprawl or suburban sprawl, which describes how people move from central urban areas to low-density areas outside of the city. Suburban communities are mostly car-dependent. Some large cities are so ‘sprawled’ out that they are almost connected to other cities that used to seem further away. Below we can see a NASA photo that shows the metropolitan areas of the Northeast. This demonstrates the urban sprawl, with the lights illustrating cities and their sprawling suburbs.

We’ve talked about cities and urban growth, but what happens within a city? People who study how residents in the cities adapt to their environments are called urban ecologists. They are very much like ecology biologists who study the relationship between animal behaviors in connection with their environment. Urban ecologists focus on the social and spatial context—how industries are distributed within the city or how the city is spatially organized, and how this relates to city residents. Like ecologists, urban ecologists think that cities form as a result of natural growth. This natural growth refers to urban expansion, immigration, and succession (new people moving in and replacing those that move out), and this is very much related to geography and the natural environment of a city. Cities may become disorganized when newcomers or immigrants move in, but it will gradually become organized again after a period of time. During these transitional changing periods, the city may suffer from more crime and other social problems in areas with the most movement of incoming and outgoing people.

Below are three models of urban growth developed by urban sociologists in the US. In general, a city grows from the center, then outwards. In the concentric zone model, Zone 1 is the central business district (CBD). Zone 2 is a transitional area containing rooming houses and deteriorating housing which breed poverty, disease, and vice. Zone 3 is the area thrifty workers have moved in order to escape the transitional Zone 2 yet maintain convenient access to their work. Zone 4 contains more expensive apartments, hotels, single-family home, etc. Commuters live in Zone 10 which consists of suburbs or satellite cities that have popped up around transportation routes. Have you ever been to Chicago? This is similar to the early city setup of Chicago, and most other traditional US cities with clear central business districts. But as transportation became more developed, ‘zones’ have also become less obvious. For example, Los Angeles is an example of a city without clear ‘zones’ since it is so spread out.

The sector model is an updated version of the concentric zone model. Concentric zones can contain different sectors, one of working-class homes, another of expensive housing, and one of businesses, etc., all competing for the same land. This model takes into account transportation developments. Cities also expand outwards, but along railways, highways, and water. Lower-income housing can be found along railroads or bordering manufacturing and industrial sectors. Chicago today is closer to this model than the original concentric zone model. Calgary in Canada is also another example of a sector model city.

In a multiple nuclei model, a city may have several centers of ‘nuclei’. The model says that even if a city did begin with one CBD, it can still develop multiple smaller business districts. This model is applicable to a lot of large cities today. For example, Mumbai and Shanghai are both examples of multiple nuclei cities. Each nucleus in these cities contains a specialized activity—such as clusters of fast-food restaurants or retail districts. Areas with similar activities cluster together to draw consumers, or because land-use is similar in adjacent areas.

Of course no city perfectly fits these models. With geography, development of transportation, and innovative businesses, cities are becoming increasingly diverse. But overall, these models are great for understanding urban planning and development.

However, some people who study urbanization argue that a city is a growth machine rather than the outcomes of a natural process, unlike what urban ecologists argue. For them, urban growth is not just organized by spatial geography, and cities will not just reorganize itself after periods of disorganization. The growth machine theory points out that urban growth is driven by a coalition of interest groups who all benefit from a city’s continuous growth and expansion. For them, the growth of cities is social, political, and largely planned and intended. For example, real estate interests may be involved—when urban growth happens, some groups benefit because properties increase in value. How groups lobby or manipulate the government or other groups, determine how cities grow and take shape. How people within the city are distributed is not so much related to geography, transportation, or space, but rather to the social actions of interest groups.