Denver (officially, The City and County of Denver) is the capital and most populous municipality of the U.S. state of Colorado. Denver is located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains. The Denver downtown district is located immediately east of the confluence of Cherry Creek with the South Platte River, approximately 12mi (19km) east of the foothills of the Rocky Mountains. Denver is nicknamed the Mile-High City because its official elevation is exactly one mile (5,280ft or 1,610m) above sea level, making it one of the highest major cities in the United States. The 105th meridian west of Greenwich, the longitudinal reference for the Mountain Time Zone, passes directly through Denver Union Station. Denver is ranked as a Beta- world city by the Globalization and World Cities Research Network. With a 2015 estimated population of 682,545, Denver ranks as the 19th-most populous U.S. city, and with a 2.8% increase in 2015, the city is also the fastest growing major city in the United States. The 10-county Denver-Aurora-Lakewood, CO Metropolitan Statistical Area had an estimated 2015 population of 2,814,330 and ranked as the 19th most populous U.S. metropolitan statistical area. The 12-city Denver-Aurora, CO Combined Statistical Area had an estimated 2015 population of 3,418,876, which ranks as the 16th most populous U.S. metropolitan area. Denver is the most populous city of the 18-county Front Range Urban Corridor, an oblong urban region stretching across two states with an estimated 2015 population of 4,757,713. Denver is the most populous city within a 500-mile (800km) radius, the most populous city in the Mountain West and the second-most populous city in the Southwestern United States after Phoenix, Arizona. In 2016, Denver was named the best place to live in the USA by U.S. News & World Report.