Evaluation Of Green Space Accessibility And Layout Optimization In Changsha Based On Path Distance

Urban Green Space is an important part of the urban ecosystem,not only for beautifying the city,but also for improving the quality of the urban environment and optimising the urban ecosystem.It includes various vegetation,open space and urban parks,among which urban parks have a variety of functions and play an important role in urban green space.In the context of rapid urbanisation and the great importance China attaches to the construction of ecological civilisation,how to adopt scientific means to evaluate the service level of urban green space and improve the layout of urban green space in a scientific and reasonable manner is a problem that needs to be solved to promote urban green development.In order to present the distribution pattern of urban green space supply and demand in a more comprehensive manner,and provide a basis for the optimisation of urban green space layout.This study takes the municipal district of Changsha as the research object,carries out urban green space accessibility analysis from two perspectives of global green space and urban parks based on path distance,and gives suggestions for green space layout optimisation based on the analysis results.The conclusions of the study are as follows:(1)Research model construction for urban green space accessibility:the overall layout of urban green space is analysed using nuclear density,green space coverage and landscape pattern index.The container method was used and indicators such as green space area,green space shape complexity,green space aggregation and normalised vegetation index were utilised to measure the global green space accessibility.The accessibility of urban parks was calculated using an optimised Gaussian two-step moving search method.The results of the accessibility metric are combined with the population distribution,and the location entropy is used to reflect the social equity of green space.(2)Global green space and urban park spatial distribution characteristics:the green space coverage rate of Changsha city district is 63.75%,and the green space coverage rate gradually increases from the city centre to the city edge.The degree of landscape fragmentation of green space in the urban centre is high,the diversity of landscape patches is poor,and the complexity of patch shapes is high.The urban fringe has a lower degree of landscape fragmentation,a better diversity of patches and a lower complexity of patch shapes.The urban parks in Changsha city district are clustered and have an unbalanced spatial distribution.(3)Accessibility of global green space and urban parks:The accessibility of global green space in Changsha City gradually increases from the urban centre to the urban fringe,and the accessibility of green space in the urban fringe is better.The accessibility of urban parks increases and then decreases from the urban centre to the urban fringe,and the high value of urban park accessibility is concentrated near the city’s comprehensive parks,with the larger parks providing more services.The matching results show that the urban centre is mainly the area where urban park accessibility is dominant,while the urban fringe is dominated by global green space accessibility.(4)Fairness of global green space and urban parks:the global green space location entropy value shows a trend of gradually increasing from the city centre to the city edge,and the high value of urban park location entropy is concentrated in the vicinity of the comprehensive urban park.There is a certain inequity in the distribution of both green space and urban parks in the Changsha city district.The matching results of the two show that areas where both global green space locational entropy and urban park locational entropy are less than one are mainly concentrated in areas with higher population density in the city centre;areas where both global green space and urban park locational entropy are greater than one are mainly concentrated near large urban comprehensive parks;more areas where global green space equity is better than urban park equity appear in urban fringe areas.(5)Optimisation of urban green space layout:Based on the results of accessibility and fairness metrics,suggestions are made to optimise the layout of green space in response to the problems in different areas,explore potential green spaces and promote the construction of micro parks;improve the quality of green spaces and enhance the accessibility of green space;ensure regional balance and optimise the function of green space.The K-means algorithm is used to identify the number of proposed parks,and the PSO algorithm is used to select sites for proposed parks.15 areas are selected for priority urban park additions,and then after feasibility analysis and demonstration,the results show that it is feasible to use the K-means algorithm and PSO algorithm for urban park site selection.