Sudan is located in northeastern Africa. It borders the Red Sea between Egypt on the north and Eritrea and Ethiopia on the southeast; it borders Chad and the Central African Republic on the west. It is the largest country in Africa.

The total area of the country is 2,505,813 square kilometers, with 2,376,000 km² land, and 129,810 km² water. This is slightly larger than one-quarter the size of the United States, one-fifth the size of Europe, and one-third the size of Australia.

The Nile is the dominant geographic feature of Sudan, flowing 3,000 kilometers from Uganda in the south to Egypt in the north.  Most of the country lies within its catchment basin. The Blue Nile and the White Nile, originating in the Ethiopian highlands and the Central African lakes, respectively, join at Khartoum to form the Nile River proper that flows to Egypt. 

Northern Sudan, lying between the Egyptian border and Khartoum, has two distinct parts, the desert and the Nile Valley.  To the east of the Nile lies the Nubian Desert; to the west, the Libyan Desert. They are similar--stony, with sandy dunes drifting over the landscape. There is virtually no rainfall in these deserts, and in the Nubian Desert there are no oases. In the west there are a few small watering holes where the water table reaches the surface to form wells that provide water for nomads and caravans. Flowing through the desert is the Nile Valley, whose alluvial strip of habitable land is no more than two kilometers wide and whose productivity depends on the annual flood.

Western Sudan is a generic term describing the regions known as Darfur and Kurdufan that comprise 850,000 square kilometers. Traditionally, this has been regarded as a single regional unit despite the physical differences. The dominant feature throughout this immense area is the absence of perennial streams; thus, people and animals must remain within reach of permanent wells. Consequently, the population is sparse and unevenly distributed. Sudan's third distinct region is the central clay plains that stretch eastward from the Nuba Mountains to the Ethiopian frontier.  The central clay plains provide the backbone of Sudan's economy because they are productive where settlements cluster around available water. 

The southern clay plains extend all the way from northern Sudan to the mountains on the Sudan-Uganda frontier, and in the west from the borders of Central African Republic eastward to the Ethiopian highlands. This great Nilotic plain is broken by several distinctive features. First, the White Nile bisects the plain and provides large permanent water surfaces such as lakes. Second, the Sudd, the world's largest swamp, provides a formidable expanse of lakes, lagoons, and aquatic plants, whose area in high flood waters exceeds 30,000 square kilometers, or approximately the size of Belgium.

Information source from Wikipedia.