The dominant physical features is the rugged cordilleras that splay out from the Himalayas to the north and are to the south. These north-south trending of mountains chains have been heavily weathered and rounded in the tropical rainy climate. The ranges are parallel to one another, separated by the major river basins. These river basins are the corelands. The mountain ranges are the Annamite chain of Vietnam, the Shan highlands of western Thailand and eastern Burma extending to Main peninsula and the Arakanyoma of Western Burma. Irrawady, Salween, (Burma) Menam (Thailand) and Mekong (Kampuchea and Vietnam) are the main river basins.
In contrast to this stability and regularity of the mainland mountain chains, the younger active belt of volcanism is associated with the south East Asia’s islands. It is a part of circum-Pacific belt of volcanism stretching from Sumatra and Java eastward to Celebes, the Moluccas and northward to the Philippines. Thousands of islands in the Indonesia and Philippines areas have their own contribution on the physiography of the region. Both Monsoon and tropical climates prevail here. In short, it may be said that this region of the world is distinct in its climatic characteristics, typical physiography, economic, overtures and cultural pattern.
Despite diversity in landforms, they shared maritime orientation and tropical climate giving south East Asia a similar pattern of economic growth and development. It is a sparsely populated region among the states of Monsoon Asia. There are pockets of high concentrations such as parts of the island of Java and Luzon, the lower deltas of the Irrawaddy, the Menam, ChaoPhraya, the Mekong and the rivers and the city state of Singapore. The density varies from 300-750 persons per square kilometer.
The capital cities like Rangoon, Bangkok, Djakarta and Manila are the example of the primate cities. The urban centres are Saigon-Choon Hanoi, Singapore and Kuala Lumpur. The under-populated areas cover high mountains, thick forests, swamps, and large tracts of poor soil in eastern, Sumatra, Inland Borneo, southern Philippines, Interior parts of Burma, Indo-China and Thailand. The least density areas have one person per square kilometer. The moderate density, areas are western kialaya and southern and north western Java. Here the density ranges from 100 to 300 persons per square kilometer.