To Compare

Cities, Size, Scale, and Form

Coastlines, lakeshores, rivers, and mountain ridges are chiefly responsible for the shape of cities. Views from space suggest that even the largest of the world's great cities were shaped by their natural location. The ground plain for the city of Los Angeles originated through crustal upheaval, and the rivers that emerged on its slopes have almost disappeared, but on a satellite image the shape of the large drainage basin that the city occupies is impressive and understandably its most important form-giving element.

Only recently have new parts of Cairo started to climb away from the Nile River valley onto the rim of the Sahara desert, where they have begun to encroach on the pyramids. Likewise, Shanghai has only recently crossed the Huangpu River, even if future satellite images will almost certainly show it stretched out onto the large fertile plain of the Yangtze River Delta.

As urban population grows, it will be highly relevant to watch the cities of this world from space—and not only the expanding cities of the developing world but also the dispersing cities in the developed world. If one were to imagine for a moment that it would be possible to direct the growth of cities in the developing world—that is, not to stop the influx of rural migration but to direct the renewal and expansion at their outskirts—future satellite images would show a web of linear gaps in settlement patterns, where now continuous urbanization occurs. These gaps would coincide with the existing water drainage patterns.

For reasons that we well understand, new urbanization would stay at a distance from water: from creeks, rivers, bays, and estuaries. Of all physical measures, the preservation of land near water would provide the greatest benefits for human health, health of vegetation and animal life, quality of the air, and a more comfortable climate.

The same understanding of natural systems would direct the dispersed cities in the developed world. In both worlds, the result would lead to a better integration of cities with the forces of nature. This concern for the integration of natural processes into city design will surface again in other chapters of this book.

The second major theme of the book relates city form to human experience. The comparison of city maps in this chapter helps us reflect on the quality of life in cities. The primary urban resource, the amount of space available to each individual, is stunningly variant. The comparison between the maps should not lead us to the conclusion that more space equals a higher or better quality of life; rather, we should conclude that land is a precious resource, to be used deliberately and not to be wasted.

At first disbelief sets in when the maps of the San Francisco Bay Area are shown next to Hong Kong, and next to a map of the Randstad, the urban concentration in The Netherlands that forms a ring and includes Amsterdam, Utrecht, The Hague, and Rotterdam. The comparison suggests that all inhabitants of the San Francisco Bay Area could live together in Sausalito and the urbanized areas of a small county to the north of San Francisco under conditions Bay Area residents would find extremely uncongenial, that is, if they were to live on the same land area and at the same density as the seven million people of Hong Kong. The rest of the Bay Area would be unpopulated. When shown to Bay Area residents the comparison produces a sense of shock and disbelief. All three maps were reproduced at the same graphic scale; all three show urbanized regions that accommodate nearly the same number of inhabitants, seven million people. The comparison is made possible by computing the surface of each of the three urbanized areas and expressing it as a percentage of a fifty by fifty kilometer square.

In the year 2000 when this collection of maps was started, the population of the San Francisco Bay Area was approaching seven million people and covered 83.75 percent of such a square; Hong Kong has since exceeded seven million inhabitants, but it still covers only 6 percent of a fifty by fifty kilometer square, whereas the Randstad in The Netherlands with its 6.6 million covers 42.7 percent of the same size square. Cities in different cultures with relatively equal numbers of inhabitants accommodate people at strikingly different densities. The conditions associated with the high density of Hong Kong are quickly explained. They are chiefly related to history, the influx of refugees from mainland China, and the political status of the former British colony. But the reasons for the high density are also explained by reflecting on Hong Kong's topography. Most of the available and buildable land area is urbanized. The same is true for the San Francisco Bay Area; topography defines the extent of urbanization. Since the Bay Area has so much more buildable land, it is used at a dramatically different density. The Randstad on the other hand makes for a different comparison; the Rhine–Meuse–Scheldt Delta has much open land available, but by comparison the cities of this urbanized region have only modestly expanded into the agricultural land. The collective political will has limited the extent of the urbanization. Historically, all land above water was precious and had to be protected from flooding. As a result, residents here have lived at relatively high densities because they have also lived in settlement patterns barely at sealevel, frequently below.

It is fair to conclude from the comparison of the three urban regions that human tolerance for density varies significantly, but the metrics of density as they relate to human ecology are not very well understood. Thus the comparisons between available space in cities and numbers of people using it allow us to interpret human population as part of the earth's ecosystem.

It is possible to apply other metrics, in addition to geographic size, to a comparison between these three urban settlements; for example, car ownership, average length of journeys to work, number of trips made by public transit, air quality, per capita energy consumption, human health statistics, distance to open space—in short, all measures that attempt to quantify sustainable life in cities. Some of this work had its beginning in a metropolitan world atlas. For example, the atlas compares trips by public or private transportation. Hong Kong residents use transit for 61 percent of their work-related trips, Randstad residents for 49 percent, and Bay Area residents for only 4.7 percent. According to the atlas, the carbon monoxide (CO) emissions for the Bay Area amount to 313.3 tonne per square kilometer, double the CO emissions of Randstad's 167 tonne. But Hong Kong's emissions are 757.9 tonne. In making these comparisons we might not always find direct causality in relation to density and spatial distribution of...