The Study Of Accessibility Based On The Floating Trajectory Data

The fairness of people enjoying public service becomes more and more concerned by people and government with the development of society.As an indicator of public service equity evaluation,accessibility has become a hot topic in the fields of geography,urban design and transportation.Accessibility the ease with which activity locations or urban services can be reached from a particular location or by an individual.In the study of public service accessibility,the demand size of people's unit,the supply capacity of the service facilities,and the connectivity between people's unit and service facilities become the main impact factors.Especially the connectivity between people's unit and service facilities,which reflects the ease of accessing public service by overcoming spatial barriers become the focus in the study of accessibility.While the characteristics of people's travel behavior which has a subjective consciousness in the process of human-earth interaction are often be ignored.As a result,the accessibility can only reflect the theoretical level of the ease that a location accessing a service,instead of the actual level.That is to say,the authenticity of accessibility is not as high as we might think.In view of this problem,the accessibility evaluating method that takes into account human travel behavior is proposed in this study.The travel behavior characteristics was extracted from people's travel activities and quantified as the human-earth interaction factor,and then this human-earth interaction factor is applied into the accessibility evaluation method to improve the authenticity accessibility results.However,due to data privacy and business interests,explicit data related to people's travel activities is difficult to obtain directly.While the floating trajectory data which contains abundant travel behavior information can make up for this deficiency.Therefore,the accessibility evaluation method which takes into account the travel behavior characteristics is focused based on the floating trajectory data in this study.The main contents and conclusions of this paper are as follows:(1)A scalable space-time cube model based on sub-trajectoriesA method for the management of trajectory data under three-dimensional space,which is a scalable space-time cube model based on sub-trajectory object.The sub-trajectory is extracted from floating trajectory data and organized with origin(O),destination(D)and time(T)in three dimensions.Then,the space-time unit is combined with semantic scene and the space-time cube model oriented the sub-trajectory object is set up to simulate the O,D and T of sub-trajectory in space-time context.The basic unit of the space-time cube has scalability,which not only provides extensibility for the analysis and calculation at different scales,but also facilitates the application of different size of trajectory data.(2)An empirical space barrier measurement under space-time constraintsIn this study,the frequency of sub-trajectory under space-time constraint instead of the total frequency without constraint is taken as the experience of the road segment.Then,a space-time constraint experience model(STCEM)is constructed through combining the experience of road segment with the length and travel time of it.Next,based on STCEM,the empirical road network under space-time constraint is established and the spatial empirical barriers could be calculated by this road network.Results show that the STCEM proposed in this study can simulate the actual travel route of people with the highest trajectory coverage.Meanwhile,the travel time,distance and speed were also taken into account into STCEM.Compared to the unconstrained experience model(EM),the trajectory coverage,travel time,travel distance and travel speed reflect the advantage of 86.7%,93.3%,86.7% and 76.7% respectively.(3)An integrated access probability field model which takes into account the travel behavior characteristicsAn access probability field model based on grid is established and the uncertainty of people's accessing a public service is expressed by the access probability of spatiotemporal unit to the service,instead of the space barrier.The factors that affect people's access to public service is abstracted to objective and subjective aspects,and represented as experience barrier model based access probability(MAP)and trajectory data based access probability(DAP)respectively.Then the MAP and DAP are integrated into a unified framework using the raster algebra and an integrated access probability(IAP)field which contains double factors of objective and subjective is established.The results show that the IAP field can not only describe the distribution of all service facilities' attractive in the study area,but also analyze the willingness of access service facilities from any spatiotemporal unit.(4)The accessibility evaluating based on the integrated access probability field modelThe accessibility evaluating method of two-step floating catchment area method(2SFCA)and enhanced two-step floating catchment area method(E2SFCA)are focused on in this paper and the calculation of catchment area and its sub-zones are improved.Based on the integrated access probability field model,the multi catchment areas of service facilities under different access probability thresholds are generated using the contour creating tool,and then the sub-zones were extracted according to the characteristics of the catchment areas.Finally,the accessibility of Shenzhen 3A-hospital was evaluated based on 2SFCA and E2 SFCA method,respectively,to verify the effectiveness of our method.The results show that the catchment areas based on the IAP field has stronger expression ability than that based on the spatial barriers because it could adapt to different situation such as unbalanced facilities distribution,different reputation of service facilities,different type of service facilities and unbalanced distribution demand.Importing this catchment area into 2SFCA and E2 SFCA methods,the results of accessibility show more details than that calculated solely by travel barriers,furthermore,the distribution of accessibility also presents more imbalanced distribution than traditional methods.