Asia is the largest region in the world with 30 percent of the land mass and 60 percent of the population. Given its vast geographical expanse, Asia and the Pacific is perhaps also the most diverse region in terms of economy, society, culture, environment, and human settlements. Geographically, the 63 countries and territories in the region have been grouped into five subregions: East and North-East Asia, South-East Asia, South and South-West Asia, North and Central Asia, and the Pacific. The vast spread of the Asia-Pacific region features high-, middle- and low-income economies, as well as a wealth of diverse societies and cultures. The region’s environment also presents a varied picture with tropical and temperate climates, and some of the world’s most arid and water-rich biomes, not to mention the highest mountains (the Himalayas) and gigantic river valleys and deltas (those of the Brahmaputra, Ganges, Indus, Irrawaddy, Mekong, Red, Yangtze, and Yellow rivers). Finally, about human settlements, the region is host to highly urbanized countries such as Australia, New Zealand, and Japan, and others much less urbanized such as Nepal, Papua New Guinea, and Sri Lanka.

For all the rapid demographic expansion of Asian cities, with an urbanization rate of 42.2 percent in 2010 the region ranked as the second least urbanized in the world after Africa’s 40.0 percent, although half the world’s urban population now lives in Asian-Paciic cities. In 2010, Asian cities were home to 1.76 billion people. While the world became predominantly urban in 2008, Asia is not expected to reach the 50 percent mark before 2026. The number of mega-cities (those with populations of 10 million or more) is increasing and half (12 out of 21) are now in the Asia-Pacific region. Moreover, mega urban regions, urban corridors, and city regions reflect the emerging links between city growth and new patterns of economic activity.