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, with regard to 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.