Quito, officially San Francisco de 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 Pichincha, an active stratovolcano in the Andes mountains. With a population of approximately 1,397,698 in the decadal national census of November 25, 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 residents in 2001, and the capital of the Pichincha province. Quito is also to be the headquarters of the Union of South American Nations from 2008.The elevation of the city's central square (Plaza de La Independencia or Plaza Grande) is 2,850 m (about 9,350 ft), making Quito the second highest capital city in the world. Quito is located about 25 km (15 miles) south of the equator. A monument and museum marking the general location of the equator is known locally as la mitad del mundo (the middle of the world), to avoid confusion, as the word ecuador is Spanish for equator.Due to its high altitude and position on the equator, Quito has a constant, mild to cool climate.