Foreign studies on the metropolitan

Foreign studies on the metropolitan area mainly focus on the theoretical concept of metropolitan area and its development. In terms of the concept of metropolitan area, foreign cities started to develop earlier, so there are more research results on the concept of metropolitan area. Through the collection and integration of foreign relevant literature, foreign research on the concept of metropolitan area can be divided into the following stages: the first is the enlightenment stage from 1915 to 1945. Howard E put forward the concept of "composite group", arguing that metropolitan area is an urban composite group formed on the basis of location, industry type, resource type, etc. Geddes P (1915) studied the evolution of urban agglomerations and proposed the evolution effect of urban agglomerations according to their different development stages and levels. Unwin R equates urban agglomeration to the collection of different cities and believes that the formation of urban agglomeration is usually based on the same types of industrial elements and resources. The second is the initial stage from 1945 to 1970. At this stage, after the end of World War II, the urbanization of various countries continued to advance, which enhanced the radiation effect of the metropolitan area and expanded the size of the metropolitan area. Vining R believes that the development of urban circle is a complex system project. The development of urban circle usually not only depends on economy, but also is closely related to the social and spatial development of the city. The third is the rich stage from 1970 to 1985. At this stage, with the continuous expansion of the economic aggregate and population agglomeration scale of the metropolitan area, the metropolitan area continues to develop and expand. Therefore, scholars in this period started from the spatial deepening of urban agglomeration, studied the population agglomeration and industrial transfer, and focused on the relationship between urban and rural integration zone and urban agglomeration. Lynch K, Rondinelli Da and other scholars on the relationship between industrial transfer, economic aggregate and population migration