Ethiopia is located in northeastern Africa, and is officially called the Federal Democratic Republic of Ethiopia. It is surrounded by the countries of Somalia, Kenya, Sudan, Eritrea, and Djibouti. Ethiopia has over 70 ethnic and linguistic groups, and is the oldest independent nation in Africa. Ethiopia covers over 400,000 square miles, and has terrain including mountains, deserts, and plateaus. Agriculture is the country's chief economic activity, and is carried out on the plateaus. The climate varies greatly according to elevation. There is a tropical zone, which has an average annual temperature of around 80 degrees, the subtropical zone on the highland plateaus has an average temperature of about 72 degrees, and the higher elevations which has an average temperature of 61 degrees. There is a rainy season from June through September. Ethiopia has over 58 million people according to a 1998 estimate. 86 percent of these Ethiopians are supported by agricultural occupations. Ethiopia is very diverse, and is divided into nine regions, which separates the major ethnic groups. Addis Ababa is the capital and the largest city in Ethiopia; however, only 16 percent of the population is classified as urban. Ethiopia is one of the world's poorest countries, with a per-capita gross domestic product of $110 a year. Elevation and geographic location produce three climatic zones: cool zone above 2,400 meters where temperatures range from near freezing to 16° C; temperate zone at elevations of 1,500 to 2,400 meters with temperatures from 16° C to 30° C; and hot zone below 1,500 meters with both tropical and arid conditions and daytime temperatures ranging from 27° C to 50° C. Normal rainy season from mid-June to mid-September (longer in the southern highlands) preceded by intermittent showers from February or March; remainder of year generally dry.