Located in southwestern Africa, Angola is one of the important sea passages of central and southern Africa. With a coastline of 1,650 kilometers and a land area of 1,246,700 square kilometers, it has a savanna climate in most of its northern part, a subtropical climate in the south and a temperate climate in the high-altitude areas. It boasts abundant oil, natural gas, minerals and forest resources, and aquatic products. Oil production and diamond mining are the pillar industries of Angola's national economy. Angola is the second largest oil producer in Africa and its oil is mainly exporting to China, the United States, India, South Africa, Portugal and other Eurasian countries. In 2017, Angola’s annual output value of diamonds (gross diamonds) was 1.105 billion US dollars, and the diamond revenues accounted for 1% of its domestic GDP. The country is divided into 18 provinces and further subdivided into 164 cities. It has a population of 25.79 million, and an average population density of 20.6 inhabitants per square kilometer. Luanda Province, the capital of Angola, is located on the east coast of the Atlantic Ocean. It is the largest city in the country with a population of over 7 million. As the largest port and the political and economic center of Angola, it covers 60% to 80% of Angola's economic activities. With the official language being Portuguese, about 42 national languages are spoken in Angola, Umbundu (central and southern region), Kimbundu (Luanda and inland region), Kikongo (northern region) and Bant.