Analysis On The Structural Fractal Of Artificial Ground Cover Patches In Chinese Cities

Land is the most important resource and carrier of a city,and land use behavior is an important factor that affects or even determines the development of a city.Under the background of rapid urbanization,urban land use,especially the types of artificial land cover,changes rapidly and has diverse combinations.Fractal is the optimized structure of nature.Together with allometric growth,it is known as the "fourth dimension" of life.As the "fourth generation language" of geography,fractal essentially reveals the spatial complexity of geographical phenomena and things,and many geographical events have been found to have geometric fractal characteristics.In recent years,urban research has gradually shifted from focusing on form,location and place to focusing on association and flow.Structural fractal,one of the three characteristics of complex networks,has also been introduced into geography to reveal the complexity and diversity of the ways in which geographical events are related.Studies have shown that urban land use is a typical geometric fractal body.Because form affects structure,structure determines function.It seems natural to think of: Is land use a structural fractal like a road network? What are the differences in fractal characteristics of land use structure in different cities? What are the similarities and differences between the fractal features of urban land use structure and road network structure?In order to answer the above questions,this thesis collected artificial land cover data and12 related physical geography and socio-economic indicators of 346 cities in China,constructed an artificial land network model based on the Voronoi diagram.A variety of structural fractal analysis methods are used to excavate the structural fractal and self-similar characteristics of the urban artificial land cover,reveal its influencing factors and common characteristics,and analyze the similarities and differences of the structure fractal characteristics of the road network and artificial ground surface.The research results show that the fractal characteristics of the urban artificial land cover structure are obvious.The fractal dimensions of box-covering,volume,and degree-volume structure of 346 cities in China have value ranges [1.730,3.227],[1.456,3.090],and [1.349,2.660],respectively.Numerically,the three structural fractal dimensions all present a normal distribution,and the relationship of box-covering structure fractal dimension > volume structure fractal dimension > degree-volume structure fractal dimension is generally presented.The fractal dimensions of the three types of urban artificial land cover structures all show significant spatial autocorrelation characteristics,and there are local clusters,but they have not yet demonstrated strong regional distribution characteristics.Under multiple topological scales,the network does not show significant small-world and scale-free characteristics,indicating that the urban artificial land cover does not have the typical structural self-similar characteristics.The results of the third definition of fractal index such as Ht show that urban land use has the third definition of geographic fractal characteristics in both form and structure,and the network degree value level difference is obvious.The numerical trends of CRG and RA are consistent with the Ht index.The elevation and slope in the physical geographic factors have a weak local negative driving force on the structural fractal,and the current urban construction land and green area in the socio-economic indicators have a relatively obvious local positive driving force on the structural fractal dimension.Finally,by comparing the structural fractal dimensions between the road network and artificial land cover of the top 100 cities in population,it is found that the three structural fractal dimensions between the two have a positive correlation,indicating that the road network and artificial land cover development shows obvious characteristics of co-evolution.The relevant conclusions of the thesis are helpful to enrich the urban spatial structure theory and fractal theory,and also provide theoretical support for urban design and space optimization.