Humanity has been given a second chance: we now need to build urban areas yet again that are at least equivalent in size to the cities that we have already built, we need to do it better, and we need to do it in a very short time.(1)
Urban Growth and Sustainable Use of Space
The space taken up by urban localities is increasing faster than the urban population itself. Between 2000 and 2030, the world’s urban population is expected to increase by 72 per cent, while the built-up areas of cities of 100,000 people or more could increase by 175 per cent.(2)
The land area occupied by cities is not in itself large, considering that it contains half the world’s population. Recent estimates, based on satellite imagery, indicate that all urban sites (including green as well as built-up areas) cover only 2.8 per cent of the Earth’s land area.(3)This means that about 3.3 billion people occupy an area less than half the size of Australia.
However, most urban sites are critical parcels of land. Their increased rate of expansion, and where and how additional land is incorporated into the urban make-up, has significant social and environmental implications for future populations.
From a social standpoint, as shown in Chapter 3, providing for the land and shelter needs of poor men and women promotes human rights. It is critical for poverty alleviation, sustainable livelihoods and the reduction of gender inequalities. Most city growth will be in developing countries, and many of the new urbanites will be poor. The form and direction of future city growth, as well as the way land is apportioned, utilized and organized, are all critical for economic growth and poverty reduction. Planners and policymakers must take proactive stances, based on a broader and longer-term vision, to guarantee the rights to the city for a rapidly growing number of poor people.
The territorial expansion of cities will also affect environmental outcomes. The conventional wisdom has been that the expansion of urban space is detrimental in itself. Since many cities are situated at the heart of rich agricultural areas or other lands rich in biodiversity, the extension of the urban perimeter evidently cuts further into available productive land and encroaches upon important ecosystems.
At the same time, however, there is increasing realization that urban settlements are actually necessary for sustainability. The size of the land area appropriated for urban use is less important than the way cities expand: Global urban expansion takes up much less land than activities that produce resources for consumption such as food, building materials or mining. It is also less than the yearly loss of natural lands to agricultural activities, forestry and grazing, or to erosion or salinization.(4)
Asked the defining questions—“If the world’s population were more dispersed, would it take up more valuable land or less? Would dispersion release prime agricultural land? Would it help avoid the invasion of fragile ecosystems?”—the answer, in most countries, would be “No!” Density is potentially useful. With world population at 6.7 billion people in 2007 and growing at over 75 million a year, demographic concentration gives sustainability a better chance. The protection of rural ecosystems ultimately requires that population be concentrated in non-primary sector activities and densely populated areas.(5)
The conclusion that using land for cities is potentially more efficient only heightens the need for careful and forward-looking policies, in light of the rapid doubling of the urban population in developing countries. This chapter looks at current patterns of urban territorial expansion and their implications. It proposes putting more effort into orienting urban growth, thus allowing cities to contribute to social development and sustainability.
This proposal calls for a vision based on solid analysis, and encompassing a broader notion of “space” than the one imposed by political and administrative city limits. It also demands a longer time horizon than the terms of politicians or administrators.