Quito, officially San Francisco e Quito, is the capital of Ecuador in northwestern South America. It is located in north central Ecuador in the Guayllabamba river basin, on the eastern slopes of the Pichincha , an active stratovolcano in the Andes mountains. With a population of approximately 1,397,698 in the decadal national census of November 24, 2001, and, as estimated by the municipality, approximately 1,504,991 in 2005 , Quito is the second most populous city in Ecuador, after Guayaquil. It is also the seat of the Quito Metropolitan District, also known as Quito Canton, home to 1,842,201 million residents in 2001, and the capital of the Pichincha province. Quito is also to be the headquarters of the Union of South American Nations since 2008.