Sudan is located in tropical northeastern Africa bordering the Red Sea between Egypt in the north and Eritrea and Ethiopia to the east. It also borders Libya to the northwest, Chad and the Central African Republic in the west and South Sudan immediately to the south. Sudan, including South Sudan, was until July 2011 Africa's largest country with a total area of 2,505,813 km2 (incorporating the Suakin Archipelago in the Red Sea) of which 5.2% comprises water. The approximate area of the D.R of (North) Sudan is 1,890,000 km2 still making it the third largest country in Africa, and the terrain consists of a vast plain bounded on three sides by mountains. The isolated Nuba Mountains rise abruptly in the south-central region of this plain and the lone Boma Plateau occurs near the Ethiopian border. Most of the country lies within the catchment basin of the River Nile. The Jabal Hadid plateau in the south and west constitutes the Congo-Nile watershed. Northern Sudan is desert bisected by the Nile valley. To the east of the Nile lies the Nubian Desert; to the west, the Libyan Desert. The Nilotic plain in the south, which is drained by the White Nile from the equatorial lakes, is host to the world's largest swamp (The Sudd), whose area in high flood exceeds 30,000 km2. The central clay plains between the Blue Nile and the White Nile provide the backbone of Sudan's agricultural economy.


Sudan is largely underlain by Precambrian rocks in the centre and northeast, which were almost exclusively reactivated during the Neoproterozoic Pan-African tectono-thermal event (Mozambique Belt Orogeny). Large areas in the north are covered by continental clastic sequences of the predominantly Mesozoic Nubian cycle. Tertiary and younger basalts occur along the eastern border zone related to relatively recent activity from the East African Rift System (EARS). In very broad terms the geology of the country comprises largely unexposed cratonic basement of the Darfur, Bayuda and Nubian blocks with a series of accreted volcano-sedimentary terranes and ophiolites in the northeast exposed in the Red Sea hills; where intrusive Pan-African granitoids are numerous ranging in age from 570 - 590Ma, although some pegmatites are as young as 560Ma. A long period of pediplanation occurred after the main orogenic events and as a result unmetamorphosed Palaeozoic and Early Mesozoic rocks are uncommon in Sudan. The oldest major unit exposed comprises clastic sediments, evaporites and limestones of the Red Sea and Nubian Sandstone Groups.