From the Atlantic Ocean in the west, the Sahara extends across Africa to the Red Sea and down to the highlands of Ethiopia, surrounding an area 9,100,000 square kilometers. This ecoregion covers the central Sahara Desert, between 18° and 30° N, and has an area of 4,619,260 km2. The northern and southern margins of the Sahara, which get greater rainfall and have more vegetation cover, are described separately.The surface of the desert ranges from large areas of sand dunes, to stone plateaus, gravel plains, dry valley, and salt flats. Several deeply anatomized mountain massifs mount from the desert areas, and are presented as separate eco regions. Underground aquifers are the basics to much of the region sometimes penetrate the surface, resulting in oases.
http://www.eoearth.org/view/article/155822/
http://saharadesert2013.weebly.com/geographymapping.html
http://www.eoearth.org/view/article/155822/
http://saharadesert2013.weebly.com/geographymapping.html