The Phoenix Metropolitan Area – often referred to as the Valley of the Sun, the Salt River Valley or Metro Phoenix – is a metropolitan area, centered on the city of Phoenix, that includes much of the central part of the U.S. State of Arizona. The United States Census Bureau designates the area as the Phoenix-Mesa-Chandler Metropolitan Statistical Area (MSA), defining it as Maricopa and Pinal counties. As of the Census Bureau's 2015 population estimates, the Valley had 4,574,351 residents, making it the 12th largest Metropolitan Area in the nation by population. The gross domestic product of the Phoenix Metropolitan Area was $215 billion in 2014, 15th largest amongst metro areas in the United States.