Link to photo above: http://ppdsec.wordpress.com/2011/02/28/world-population-at-7-billion-in-2011/
Link to map: http://www.roebuckclasses.com/maps/placemap/nafricaswasia/nafricapopdensity.JPG
The population is so low in countries such as Western Sahara, Libya, and Algeria because they are located in the Sahara Dessert, which is not an ideal place for living. The population is high in Egypt because of the presence of the Nile river. Many large cities were once built around the river since it was the only source of power and water in such a vast desert, and the population has remained dense in the area over time.