Architects dig deep for cities

19.08.42: CITIES HAVE gone as high and as wide as they can: now, the challenge is to dig deep.

The message from the Third International Land Summit in Chongqing is stark. If the world is to feed itself, cities will have to expand the only way they can - downwards. Agreement between heads of state on global land use is expected soon, with legislation to apply worldwide.

At the end of the 20th century, tower blocks were springing higher and higher, but cities also continued to spread, with the pollution and loss of vital agricultural land that entailed. South China's Pearl River Delta - a megalopolis formed by the merger of the cities of Hong Kong, Guangzhou, Shenzen, Guangdong, Macau and points in between - became a major source of pollutants. Malaysia, Indonesia, Australia, South America and South Africa quickly developed their own black-spot city clusters.

The new directive aims to halt city sprawl. Every new buildi