As the largest and most populous continent in the world with just over 3.8 billion people, Asia is composed of a wide variety of ethnic groups, cultures, environments, economics, historical ties, and governmental systems. Geographically the continent makes up 8.7% of the Earth's total surface area, and 29.5% of its land area. The Arctic Ocean and a handful of seas front the northern border, while the Bering Sea separates Asia from North America. In the southwest the Red Sea and isthmus of Suez separate the continent from Africa. The Indian Ocean fronts most of Asia's southern borders, along with a series of bays, gulfs and seas, as well as extensive chains of both inhabited and uninhabited islands.
The history of Asia can be seen as the distinct histories of several peripheral coastal regions: East Asia, South Asia, Southeast Asia and the Middle East, linked by the interior mass of the Central Asian steppes. The coastal periphery was home to some of the world's earliest known civilizations, each of them developing around fertile river valleys. The civilizations in Mesopotamia, the Indus Valley and the Huanghe shared many similarities. These civilizations may well have exchanged technologies and ideas such as mathematics and the wheel. Other innovations, such as writing, seem to have been developed individually in each area. Cities, states and empires developed in these lowlands.
The Climate of Asia is moist across southeast sections and dry across much of the interior. Some of the largest daily temperature ranges on Earth occur in western sections of Asia. The monsoon circulation dominates across southern and eastern sections, due to the presence of the Himalayas forcing the formation of a thermal low which draws in moisture during the summer. Southwestern sections of the continent are hot.
Asia has the second largest nominal GDP of all continents, after Europe, but the largest when measured in purchasing power parity. As of 2011, the largest economies in Asia are China, Japan, India, South Korea and Indonesia. Based on Global Office Locations 2011, Asia dominated the office locations with 4 of top 5 were in Asia, Hong Kong, Singapore, Tokyo, Seoul and Shanghai. Around 68 percent of international firms have office in Hong Kong.