Mexico City is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley of Mexico within the high Mexican central plateau, at an altitude of 2,240 meters (7,350 ft).Mexico City is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley of Mexico within the high Mexican central plateau, at an altitude of 2,240 meters (7,350 ft).