San Francisco de Quito, most often called Quito , is the capital city of Ecuador in northwestern South America. It is located in north-central Ecuador in the Guayllabamba river basin, on the eastern slopes of Pichincha, an active stratovolcano in the Andes mountains. With a population of 2,197,698 according to the last census (2001), and, as estimated by the municipality, approximately 2,504,991 in 2005, Quito is the second most populous city in Ecuador, after Guayaquil. It is also the capital of the Pichincha province and the seat of Metropolitan District of Quito. The canton recorded a population of 1,842,201 residents in the 2001 national census. In 2008, the city was designated as the headquarters of the Union of South American Nations.