Hyperarid city cartography
Introduction
The Sahara or Sahara (both accentuations are valid in Spanish;[1] in Arabic: aṣ-Ṣaḥrāʾ al-Kubrā, "the Great Desert"; in Amazig, ⵜⵉⵏⵉⵔⵉ Tenere or Tiniri) is the largest hot desert in the world and the third largest after Antarctica and the Arctic.[2] With more than 9,400,000 km² of surface,[3] it covers most of northern Africa, occupying a third of the total continent and an area almost as large as that of China or the United States. The Sahara extends from the Red Sea, including parts of the Mediterranean Sea coast, to the Atlantic Ocean. To the south, it is bounded by the Sahel, a belt of semi-arid tropical savanna that makes up the regions that cover northern sub-Saharan Africa.
Some of the sand dunes of the Sahara can reach 193 m in height.[4].
Etymology
The word "Sahara" comes from the transliteration into European languages of صحراء, which in Arabic means desert, resulting in a tautoponym whose closest pronunciation is [Sájara].[5][6] However, the traditional and most common pronunciation in America follows the phonetic rules of Spanish, namely, the silent "h", and the word is plain instead of esdrújula: [Saára].[1].
Geography
Most of the rivers and streams of the Sahara are seasonal or intermittent, the only and main exception being the Nile, which crosses the desert from its source in central Africa to empty into the Mediterranean. Underground aquifers can sometimes reach the surface, forming oases, such as those of Bahariya, Ghardaia, Timimoun, Kufra and Siwa.
The central part of the Sahara is hyperarid, with little vegetation. The northern and southern ends of the desert, along with its highlands, have areas of xeric grass and scrub, with taller trees and shrubs in the wadis where moisture is concentrated.
At its northern limit, the Sahara reaches the Mediterranean Sea in Egypt and part of Libya. In Cyrenaica and the Maghreb, the Sahara borders the Mediterranean forest and scrub ecoregions of North Africa, which have a Mediterranean climate characterized by a rainy winter season. According to the botanical criteria of Frank White, as well as the geographer Robert Capot-Rey, the northern limit of the Sahara corresponds to the northern limit of cultivation of the date palm and the southern limit of esparto grass, a typical herb of the Mediterranean climate zone of the Maghreb and the Iberian Peninsula. The northern limit also corresponds to the 100 mm precipitation isoline.