The Ecology of Urban Location

What is the relationship between cities and their physical settings? At first glance, cities seem totally divorced from the natural environment. What possible relationships could the shiny glass office buildings, paved streets, and high-rise apartment buildings that characterize most cities have with forests, fields, and rivers? In this section we examine several different ways to think about the relationships between urban life and its natural setting.

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Site and Situation

Both site and situation are dynamic, changing over time. For example, in San Francisco during the gold rush period of the 1850s, the small cove was filled to create flatland for warehouses and to facilitate extending wharves into deeper bay waters. The filled-in cove is now occupied by the heart of the central business district (Figure 10.9). The geographical situation also changed as patterns of trade and transportation technology evolved. The original transbay situation was quickly replaced during the gold rush by a new role: supplying the mines and settlements of the gold country. Access to the two major rivers leading to the mines, plus continued ties to ocean trade routes, became important components of the city’s situation.

San Francisco’s situation has changed dramatically in the past two decades, for it is no longer the major port of the bay. The change in technology to containerized cargo was adopted more quickly by Oakland, the rival city on the opposite side of the bay, and San Francisco declined as a port city. Oakland was able to accommodate containerized cargo in part because it filled in huge tracts of shallow bay lands, creating a massive area for the loading, unloading, and storage of cargo containers.

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Certain attributes of the physical environment have been important in the location of cities. Those cities with distinct functions, such as defense or trade, were located because of specific physical characteristics. The locations of many contemporary cities can be partially explained by decisions made in the past that capitalized on the advantages of certain sites. The following classifications detail some of the different location possibilities.

Even more advantageous was the river-island site, which, because the stream was split into two parts, often combined a natural moat with an easy river crossing. For example, Montreal is situated on a large island surrounded by the St. Lawrence River and other water channels. The offshore-island site—that is, islands lying off the seashore or in lakes—offered similar defensive advantages (Figure 10.11). Mexico City began as an Indian settlement on a lake island. Venice is the classic example of a city built on offshore islands in the sea, as is Hong Kong. Peninsula sites were almost as advantageous as island sites, because they offered natural water defenses on all but one side. Boston was founded on a peninsula for this reason, and a wooden palisade wall was built across the neck of the peninsula.

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Danger of attack from the sea often prompted sheltered-harbor defensive sites, where a narrow entrance to the harbor could be defended easily. Examples of sheltered-harbor sites include Rio de Janeiro, Tokyo, and San Francisco.

High points were also sought out. These are often referred to as acropolis sites; the word acropolis means “high city.” Originally the city developed around a fortification on the high ground and then spilled out over the surrounding lowland. Athens is the prototype of acropolis sites, but many other cities are similarly located.

Especially common types of trade-route sites (Figure 10.12) are bridge-point sites and river-ford sites, places where major land routes could easily cross over rivers. Typically, these were sites where streams were narrow and shallow with firm banks. Occasionally, such cities even bear in their names the evidence of their sites, as in Frankfurt (“ford of the Franks”), Germany, and Oxford, England. The site for London was chosen because it is the lowest point on the Thames River where a bridge—the famous London Bridge—could easily be built to serve a trade route running inland from Dover on the sea.

Confluence sites are also common. They allow cities to be situated at the point where two navigable streams flow together. Pittsburgh, at the confluence of the Allegheny and Monongahela rivers, is a fine example (Figure 10.13). Head-of-navigation sites, where navigable water routes begin, are even more common, because goods must be transshipped at such points. Iquitos, Peru, is located at the head-of-navigation site for the Amazon River, and Minneapolis–St. Paul, at the falls of the Mississippi River, also occupies a head-of-navigation site. Portage sites are very similar. Here, goods were portaged from one river to another. (Portage means the act of carrying a ship and/or its cargo between navigable waters.) Chicago is near a short portage between the Great Lakes and the Mississippi River drainage basin. In these ways and others, an urban site can be influenced by the physical environment. But so, too, do cities change that physical environment in a multitude of ways.

Natural Disasters

In addition, many cities around the world are situated near water, so they are often located in the direct paths of multiple types of disasters, including hurricanes and tsunamis (which are often caused by earthquakes). Making matters even worse, some scientists have recently noted an increase in the occurrence of natural disasters. They attribute this increase partly to global climate change brought about by a range of human activities including deforestation, increasing industrialization, and harmful agricultural practices.

The combination of increasing urbanization and a growing number of natural disasters means that more and more people’s lives are being impacted adversely. According to the United Nations Environment Program, since the start of the new millennium, billions of people around the world have been affected by some 2,500 natural disasters (Figure 10.14). As with the Haitian earthquake, it is often poor people who are the most affected, since they tend to live in structures that are not well built and in sections of the city that are particularly vulnerable to environmental forces. In fact, in many cities in the developing world, squatter settlements populated by the poor are often situated on steep hillsides or in poorly drained low-lying areas that are highly prone to flooding, mudslides, and other disasters.

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Urbanization and Sustainability

But the environmental effects of increased urbanization—the urban footprint—can spread beyond the immediate stresses caused by higher concentrations of population. Urban living often leads to rising levels of consumption, as new urbanites gain access to better jobs and more disposable income. This growing demand for things like better food can impact areas far from urban centers. For example, as the United Nations report Unleashing the Potential of Urban Growth suggests, tropical forests in Tobasco, an area 400 miles away from Mexico City, have been turned into cattle-grazing areas in response to urbanites’ demands for meat, while, in a second example, a major contributing factor to the deforestation of the Amazon is the increased demand for soybeans from the newly urbanizing regions of China as well as from the urbanites of the United States, Japan, and Europe.

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Urbanization, however, does not necessarily imply environmental degradation. For example, the higher densities of population that cities represent can be seen as a form of sustainable growth. Half the population of the world—the urban half—lives on approximately 3 percent of the landmass. The concentration of people in cities therefore opens up other areas that can be protected and left relatively free from human use. Many countries in the developing and developed world are working on local and regional planning projects that on the one hand maintain urban boundaries and prevent sprawl and on the other hand protect natural environments outside urban areas from environmental degradation. Such urban environmental conservation projects will likely become increasingly important in future years.