Cities are expected to absorb between two and three billion additional people by the year 2050. Whether they
manage to do so sustainably depends heavily on whether they harness the efficiency advantages of
agglomeration. Agglomeration provides compactness, concentration and connectivity. More than half of the
area expected to be urban in 2030 remains to be built. Therein lies an extraordinary opportunity to make the
future city more productive and sustainable.
However, most cities are forfeiting these advantages and becoming more expansive. With cities growing spatially
faster than their populations, urban sprawl is accelerating. As a result, urbanization is becoming less efficient.
Globally, the amount of land available for agriculture, habitat and nutrient recycling is also declining. With impending
resource limits and twin climate change and food crises, we have little time to reverse this trend.
The more compact a city the more productive and innovative it is and the lower its per capita rates of resource
use and emissions. Though sprawl and density are generally two sides of the same coin, sprawl, i.e. global urban
land cover, is more feasible to measure and monitor.