Sudan lies in the Upper Nile Valley and is landlocked except for a  900km stretch of coast along the Red Sea. Its neighbours are Egypt to the north and Libya to the north-west where the political boundaries follow lines of latitude and longitude. Chad, Central Africa and Zaire lie to the west and south where the boundary follows the Nile-Zaire (Congo) watershed. To the south are Uganda and Kenya and on the east Ethiopia and Eritrea.

The total area is nearly 2.5 million km² consisting of flat plains, generally below l000m, broken by rolling hills. Mt. Kinyeti, 3187 m, in the Imatong mountains on the Ugandan border, is the highest point. In the north-east the bare, rocky Red Sea Hills overlook the narrow coastal plain and slope westward to the Nile Valley; further south the border skirts the foothills of the Ethiopian Highlands. West of the Nile the country opens out on to broad plains rising to the isolated hill masses of the Nuba Mountains and the volcanic range of Jebel Marra. The most important hydrological feature is the valley of the Nile and its headwaters, the Atbara, Blue Nile and White Nile. The Atbara and Blue Nile systems rise in Ethiopia and flow in deeply entrenched beds across the plains. During the rains, July-October ,the rivers run full and deep, but the Atbara dries out to a string of pools during the rest of the year. South of Lake No the White Nile is divided into the Bahr el Ghazal which rises in the south-west and the Bahr el Jebel whose source is Lake Victoria in Uganda and enters Sudan by a narrow valley cutting through the mountains. The Sobat joins the White Nile just above Lake No; it rises in Ethiopia and drains the south-eastern plains. These rivers meander across flat clay plains covered with vast areas of papyrus marsh and seasonal grasslands. This is the Sudd. Sudd means blockage and refers to the rafts of vegetation which periodically block the rivers. In the Bahr el Ghazal basin the country north and east of the low Ironstone Plateau is flooded from August to November and then dries out into rich grasslands known as toic which support large herds of cattle and antelope. The Bahr el Jebel/Sobat basins are less subject to flood but have a greater area of permanent swamp. In the far south-east the country passes into the rugged lava country bordering Lake Turkana. North of Lake No the White Nile is navigable throughout the year and flows in a broad valley as far as Khartoum. Northward it alternates between open stretches with terraced fields and gorge-like reaches.