A Comparative Study On The Polycentric Structure Of Plain City And Mountain City

On the one hand,the rapid urbanization has promoted the rapid economic development of our country and improved people’s living and income level,but it has also caused a series of urban problems such as traffic congestion.As an important means to solve " urban disease",the multi-center planning strategy originated from the west has been widely adopted by large and medium-sized cities in China.Whether the evolution of polycentric structure meets the planning expectation and whether the polycentric structure and function can be identified through effective ways is of great significance to the sustainable development of the city,and has become a research hotspot in the current academic circles.At present,China’s polycentric research mainly focuses on the plain cities in the eastern and coastal areas,but pays less attention to the western areas.Most of them use methods such as geo-spatial analysis and morphological analysis to carry out morphological and functional polycentricity identification and spatial performance analysis from different dimensions such as population,land use,industry,price,transportation,lighting,etc.Research theories are mostly based on the assumption of plain homogeneity and analyze the formation and development of polycentricity from the perspective of economies of scale.The formation of polycentric structure in mountain cities is not only a passive choice under the objective environment such as landscape barrier,space scarcity and ecological fragility,but also an active adaptation under the guidance of urban planning.Different terrain conditions have created a differentiated polycentric structure between mountain and plain cities.In recent years,the state has issued a series of policies to guide cities to change their development mode and optimize their spatial structure.Urban planning has also changed from the past incremental expansion to tapping the potential of the existing stock.The rise of urban big data research provides an effective way for polycentricity multi-center identification measurement and spatial performance analysis,which can finely identify the high spatial differentiation characteristics of urban.Based on the above background,this paper takes the main urban areas of Chongqing and Chengdu as research areas,and uses POI,Tencent’s easygo data,urban building boundaries and related planning and statistical data to identify and compare the polycentric structure of mountain and plain cities from a multi-dimensional perspective,and analyzes the main reasons and planning effects for the formation of multi-centers in the two cities.It is of positive significance to guide the healthy and orderly development of the two cities.The research conclusions of this paper are as follows:(1)The results and characteristics of polycentric measurement between mountain city and plain city are compared.The conclusions are as follows: Chongqing’s main city has an obvious "polycentric urban with multiple su-bcenters and urban clusters" structure.The concentration degree of elements and development scale in Jiefangbei main center and its sub-centers such as Shapingba,Yangjiaping,Guanyinqiao and Nanping are similar and higher than those in the peripheral city clusters.Under six POI types,the urban spatial structure has obvious polycentric distribution characteristics.The sub-centers with perfect functions are mainly distributed within the inner ring,but the development of business and financial centers in the periphery are relatively lagging behind.In general,the six functions of the centers at all levels are relatively perfect,and the development degree and gathering function of the peripheral Xiyong and Chayuan sub-centers need to be strengthened.Chengdu’s main city has a "polycentricity and circle layer" urban structure,with the inner side of the third ring road as the main center,and the functions of the city’s sub-center are assumed by the outer sides of the third ring road,namely,Pidu,Wenjiang,Shuangliu,Tianfu,Longquanyi,Qingbaijiang and Xindu.The spatial distribution characteristics of different POI types are similar to that of the whole.The life center is relatively mature,while the business and financial center is relatively backward in the periphery of the third ring road.The polycentric structure of the two cities has significant differences in layout,factor agglomeration and influence scope.Chongqing’s polycentric structure is relatively compact,with close distance between the main and sub centers,similar factor agglomeration capacity and relatively balanced scale.Chengdu’s polycentric structure is relatively loose,and its main and sub-centers are far away.The gathering capacity and influence range of the main center are far beyond those of the peripheral sub-centers.In terms of population,Chongqing’s centers have stronger population gathering capacity on weekends than on workday,contrary to Chengdu.The business and financial centers of the two cities have the highest degree of agglomeration among all kinds of centers.(2)Analyzing the causes of polycentric evolution of mountain cities and plain cities,the conclusion is as follows: the main driving factors of polycentric formation in Chongqing and Chengdu include economic development,urban planning and natural environment.Economic development and industrial structure evolution are the main driving forces of polycentric formation.Multi-round urban planning plays a leading role in the formation of polycentric in the study area,and natural environment is the fundamental cause of polycentric difference between the two cities.(3)Analyzing the polycentric development and planning effect of mountain cities and plain cities,the conclusions are as follows: the development of polycentric structures in Chongqing and Chengdu have all reached the expected goals of urban planning.The functions of all levels of centers in Chongqing’s inner ring are relatively perfect,and the development of peripheral groups and subcenters needs to be strengthened;Chengdu central city has formed a polycentric structure with obvious "main strong and auxiliary weak".The development level of peripheral sub-centers is far lower than that of the main center.Chongqing and Chengdu both face problems such as unbalanced spatial development,conglutination of groups/sub-centers,traffic congestion and urban sprawl.The two cities need to attach importance to the construction of public service facilities in the outer sub-centers and groups,to ease the population and industry in the core areas of the city,to strengthen the rigid constraints of the urban development boundary and permanent basic farmland,to pay attention to the intensive use of land,and to promote the sound development of the polycentric system.