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-Glendale Metropolitan Statistical Area (MSA), defining it as Maricopa and Pinal counties. As of the Census Bureau's 2014 population estimates, the Valley had 4,489,109 residents, making it the 12th largest Metropolitan Area in the nation. It is also one of the fastest growing major metropolitan areas, gaining nearly 300,000 residents from 2010 to 2014, and more than 1.2 million since 2000.