Lagos or Lagos City is the most populous city in Nigeria, with an estimated population of 21 million in 2015. Lagos is the most populous urban area in Africa. Lagos was the national capital of Nigeria until December 1991 following the government's decision to move their capital to Abuja in the centre of the country. Lagos is a major African financial centre and is the economic hub of Lagos State and Nigeria at large. The city has a significant influence on commerce, entertainment, technology, education, politics, tourism, art, and fashion in Africa. Lagos is also among the top ten of the world's fastest-growing cities and urban areas. The megacity has the fourth-highest GDP in Africa and houses one of the largest and busiest seaports on the continent. Due to the large urban population and port traffic volumes, Lagos is classified as a Medium-Port Megacity.