Abuja is located in the centre of Nigeria, within the Federal Capital Territory (FCT). Abuja is a planned city, and was built mainly in the 1980s. It officially became Nigeria's capital on 12 December 1991, replacing Lagos, though the latter remains the country's most populous city. At the 2006 census, the city of Abuja had a population of 776,298, making it one of the ten most populous cities in Nigeria. Abuja has witnessed a huge influx of people into the city; the growth has led to the emergence of satellite towns such as Karu Urban Area, Suleja, Gwagwalada, Lugbe, Kuje and smaller settlements to which the planned city is sprawling. The unofficial metropolitan area of Abuja has a population of well over three million and comprises the fourth largest urban area in Nigeria, surpassed only by Lagos, Kano and Ibadan.