What does Panzhihua Third Line mean?

Major infrastructure construction projects. Third-line construction means that in response to China's national security threat, especially the Sino-Indian border dispute, the Indian government has decided to build a series of important projects in inland areas to improve national defense capabilities and develop the economy of inland areas. As an important node of the third-line construction, Panzhihua undertakes the construction tasks of infrastructure such as airports, highways, water conservancy and electric power, so the third-line construction of Panzhihua refers to a major infrastructure construction project started in Panzhihua City, Sichuan Province, China from the late 1950s to the early 1960s.