The Southwestern United States, also known as the American Southwest, Desert Southwest, or simply The Southwest, is the informal name for a region of the western United States. Definitions of the region's boundaries vary a great deal and have never been standardized, though many boundaries have been proposed. For example, one definition includes the stretch from the Mojave Desert in California (117° west longitude) to Carlsbad, New Mexico (104° west longitude), and from the Mexico–United States border to the southern areas of Colorado, Utah, and Nevada (39° north latitude). The largest metropolitan areas are centered around Phoenix (with an estimated population of more than 4.7 million as of 2017), Las Vegas (more than 2.2 million), Tucson (more than 1 million), Albuquerque (more than 900,000), and El Paso (more than 840,000). Those five metropolitan areas have an estimated total population of more than 9.6 million as of 2017, with nearly 60 percent of them living in the two Arizona cities—Phoenix and Tucson.