The elevational pattern of most of Nigeria consists of a gradual rise from the coastal plains to the northern savanna regions, generally reaching an elevation of 600 to 700 meters. Higher altitudes, reaching more than 1,200 meters in elevation, are found only in isolated areas of the Jos Plateau and in parts of the eastern highlands along the Cameroon border. The coastal plain extends inland for about ten kilometers and rises to an elevation of forty to fifty meters above sea level at its northern boundary. The eastern and western sections of the coastal plain are separated by the Niger Delta, which extends over an area of about 10,000 square kilometers. Much of this is swampland, separated by numerous islands. The coastal plain region penetrates inland about seventy-five kilometers in the west but extends farther in the east. This region is gently undulating with elevation increasing northward and a mean elevation of about 150 meters above sea level. Much of the population of southern Nigeria is located in these eastern and western coastal plains and in some of the contiguous areas of the coast and the lower Niger Basin.