Algeria (الجزائر, Al Jaza'ir IPA: [ælʤæˈzæːʔir], Amazigh:, Dzayer [ˈdzæjər]), officially the People's Democratic Republic of Algeria, is a country located in North Africa. It is the largest country of the Mediterranean sea, the second largest on the African continent and the eleventh-largest country in the world in terms of land area. It is bordered by Tunisia in the northeast, Libya in the east, Niger in the southeast, Mali and Mauritania in the southwest, a few kilometers of the Western Sahara in the west, Morocco in the northwest, and the Mediterranean Sea in the north. Algeria is a member of the United Nations, African Union and OPEC. It also contributed towards the creation of the Maghreb Union. Constitutionally, Algeria is defined as an Arab, and Amazigh (Berber) country. Most of the coastal area is hilly, sometimes even mountainous, and there are a few natural harbours. The area from the coast to the Tell Atlas is fertile. South of the Tell Atlas is a steppe landscape, which ends with the Saharan Atlas; further south, there is the Sahara desert. The Ahaggar Mountains (Arabic: جبال هقار), also known as the Hoggar, are a highland region in central Sahara, southern Algeria. They are located about 1,500 km (932 miles) south of the capital, Algiers and just west of Tamanghasset. Algiers, Oran, Constantine, and Annaba are Algeria's main cities. Northern Algeria is in the temperate zone and has a mild, Mediterranean climate. Its broken topography, however, provides sharp local contrasts in both prevailing temperatures and incidence of rainfall. Year-to-year variations in climatic conditions are also common. In the Tell Atlas, temperatures in summer average between 21 and 24 °C and in winter drop to 10 to 12 °C. Winters are not particularly cold, but the humidity level is high.