The Sahara Desert is the largest hot desert in the world and the largest desert following Antarctica and the Artic. Most people think of hot dunes of sand when they envision a desert. However, according to the dictionary a desert is a barren area with little to no precipitation. Antarctica and the Artic are technically deserts and larger than the Sahara. The Sahara Desert covers over 3,600,000 square miles (9,400,00- sq km). In comparison, this is approximately the size of the United States or China. This makes the Sahara the largest sandy or hot desert in the world The boundaries of the Sahara Desert stretch from the Red Sea on the east, the Atlantic Ocean on the west, the valley of the Niger river on the south, to the Mediterranean Sea on the north. The desert encompasses, at least in part, the countries of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan, and Tunisia. The Nile river runs through the Sahara Desert throughout the year, but all other rivers only exist seasonally. Grasslands may be found in the northern and southern parts of the desert, but the center region is extremely arid. The geography of the desert includes tremendous sand dunes and dune fields which may be described as a sea of sand. Additionally, there are unusual and unique landforms, stone plateaus, salt flats, gravel plains, and arid valleys.