Africa is the second largest continent, covering about 11.7 million square miles, or about 10% of the world's population. It has many large rivers that flow through it, including the Nile River, Congo River, Niger River, and Orange River. Africa also contains several mountain ranges, deserts like the Sahara, and the Great Rift Valley running several thousand miles through the eastern part of the continent. The climate and vegetation vary widely from tropical rainforests to savannah grasslands.