Africa is a continent south of Europe and southwest of Asia, bounded by the Atlantic Ocean, the Indian Ocean, the Red Sea and Mediterranean Sea. Africa is one of only two continents whose mainland straddles the equator, the other being South America. Africa is joined to Asia by the Sinai Peninsula at its north-eastern corner.
Africa is the second largest continent after Asia; its land mass takes up about 30.2 million square kilometers (11.7 square miles). The continent represents about 20% of the land mass on Earth.
The Nile River, the longest river in the world, runs through Africa. The highest mountain in Africa is Mount Kilamanjaro in Tanzania at a height of 4,600 m (15,100 ft). Other notable physical features in Africa include the Sahara Desert in northern Africa, the world's largest hot desert (the Arctic and Antarctic Deserts are larger), the Atlas Mountains north of the Sahara and near the Mediterranean Sea, the Okovango inland delta, and the Great Rift Valley, a trough that spreads across much of eastern Africa.
Approximately 1 billion people reside in Africa. The African countries with the largest population are Nigeria and Ethiopia. (Incidentally, Sudan and Algeria, respectively, are the largest African countries by area.)
Many African countries have relatively young populations, which is largely a result of low average lifespans. Much of the continent, particularly southern Africa, has been hit hard by the HIV/AIDS epidemic - in some southern African countries, such as Swaziland and Botswana, over 20% of the population is infected by HIV.