为何说兰州是一线城市？

Group 1 - Lanzhou is located in the central part of Gansu province and is the geometric center of China's land area, covering an area of 13,100 square kilometers [3] - The city is characterized by its unique geographical feature where the Yellow River flows through it, creating a landscape of "two mountains facing each other with a great river flowing in between" [4] - Lanzhou has a temperate continental climate with an average annual precipitation of around 300 millimeters and an average annual sunshine duration of 2,374 hours [6] Group 2 - The population of Lanzhou has shown a steady increase, with 3.62 million in 2010, 4.36 million in 2020, and projected to reach 4.44 million by 2024 [6] - Historically, Lanzhou was a crucial transit point on the Silk Road, connecting the Central Plains to the Hexi Corridor and the Western Regions [8] - The city serves as a transportation hub in Northwest China, with multiple railways and highways intersecting, including the Lanzhou-Qinghai Railway and the G6 Beijing-Tibet Expressway [8] Group 3 - Lanzhou's urban area is elongated, approximately 30 kilometers from east to west, and varies in width from about 1 kilometer to 5-6 kilometers [9] - The Yellow River runs approximately 47.5 kilometers through the city, and Lanzhou's metro line 1 is notable for being the first subway line in China to pass under the Yellow River [11]