| Expressway system is one of the important driving factors in terms of social and economic development.It is of great significance to explore the movements of massive vehicles inner expressway system from the perspective of spatial flow,to reveal the spatial disparities and patterns of economic activities and population travels.As a common phenomenon of social behaviors,expressway spatial flows continuously accumulate spatio-temporal big data with rich information connotation.Therefore,it is essential to express various information of expressway spatial flows for geographical analysis.In the process of these analysis,it is also necessary to further summarize and aggregate all kinds of discrete implied information to different spatio-temporal units,so as to realize the comprehensive characterization and revelation of its spatio-temporal patterns and spatio-temporal processes.The existing studies about the representation of spatial flow,such as OD(Origin Destination)data,ignores various important implied information of expressway spatial flow,pays attention to individual flow records to incur a large data volume,and becomes difficult to be adopted in GIS(Geographic Information System).Hence,the representation model and analysis method for expressway spatial flow are discussed in this paper.This paper firstly discussed the basic information connotations in expressway spatial flow,to construct the multidimensional representation space of expressway spatial flow.Then,this paper proposed the multidimensional representation conceptual model and data organization model for expressway spatial flows.Based on the proposed multidimensional representation model,this paper developed the basic framework and main steps in the aggregation analysis of expressway spatial flow,then introduced the aggregation analysis patterns of expressway spatial flow according to location and time.Taking this aggregation pattern as the basic structure,this paper developed the spatial and temporal aggregation analysis method of expressway spatial flow for different geographical research objectives(analysis of spatial pattern,prediction of temporal change,detection of element association),and proved the feasibility and effectiveness of the proposed methods through different case studies.The main conclusions of this paper are as follows:(1)This paper proposes a multidimensional representation model of expressway spatial flows.By summarizing and abstracting the basic information and characteristics of expressway spatial flows,this paper constructs the multidimensional representation space for expressway spatial flow,which mainly includes seven basic dimensions:location,time,direction,distance,duration,type and quantity.Furthermore,this paper proposes the multidimensional representation conceptual model and corresponding logic model of expressway spatial flow.This paper also discusses how to utilize the proposed multi-dimensional representation model to express various kinds of important information about expressway spatial flow,including geometric information,time information and attribute information.Compared with the existing representation methods(ex.OD data),the multidimensional expression model of expressway spatial flow proposed in this study has the advantages in terms of direct expression of various information and variable granularity.(2)This paper develops the basic patterns of aggregation analysis of expressway spatial flows.According to the proposed multidimensional representation model,this paper discusses the basic framework of aggregation analysis for expressway spatial flow,which mainly includes four steps: the selection of reference dimension,unit partition of the dimension,screen of spatial flows,calculation of aggregated features,and analysis of aggregated features.Taking location and time as the reference dimension in the aggregation analysis,this study proposes the location aggregation analysis pattern and the time aggregation analysis pattern of expressway spatial flow.Each of these two aggregation analysis patterns can generate specific aggregation analysis methods according to different geographical analysis objectives,to conduct different kinds of spatiotemporal analysis of expressway spatial flow.(3)Taking the location aggregation patterns as guidance,this paper proposes two location-based aggregation analysis methods of expressway spatial flows,which are methods to analyze the geographic disparities of expressway spatial flows,and to explore static relationships between expressway spatial flows and other geographic variables.Besides,the corresponding case studies are implemented to validate the proposed location aggregation analysis method.To analyze the geographical disparities of expressway spatial flows,this paper designs different strategies to generate and calculate the aggregated features,after classifying three types of locations(including start-stop nodes,connected line between nodes,driving route).The results show that these aggregated features can be used in geographic analysis under different scenarios,including to detect the hot spots and cold spots of expressway spatial flows,to explore the spatial regularity of traffic congestion in expressway network,to revel the connection among different regions caused by expressway spatial flows.To explore the static relationships between expressway spatial flows and other geographic variables,this study designs the strategy to generate regional aggregated features,then uses regression model to detect and analyze these kinds of relationships.The results show that this aggregation method can well simulate the relationship between expressway spatial flow and regional economic level.(4)Taking the time aggregation patterns as guidance,this paper proposes two timebased aggregation analysis methods of expressway spatial flows,which are methods to predict the quantity of expressway spatial flows,and to explore dynamic relationships between expressway spatial flows and other geographic variables.Besides,the corresponding case studies are also implemented to validate the proposed temporal aggregation analysis method.To predict the quantity of expressway spatial flows,this paper uses the mathematical technique of tensor decomposition to extract the temporal aggregated series of expressway spatial flows,then uses time series model to fit and forecast the temporal aggregated series.Finally,utilizing the foretasted values of temporal aggregated series,the predicted values for the quantity of expressway spatial flows can be calculated by tensor reconstruction.The results show that this aggregation method could bring a good prediction results with a high overall accuracy,and have the advantage in terms of efficiency.To explore dynamic relationships of expressway spatial flows,this paper develops the other methods to calculate the temporal aggregated series of expressway flows,then uses the methods of multi-variable time series to explore these dynamic relationships.The vector auto-regressive model and impulse response function are used in this paper.The results show that this aggregation method could well illustrate the relationship between expressway spatial flow and urban air pollution.To sum up,this paper proposes "one representation model + two aggregation patterns + four aggregation analysis methods",and applies the proposed contents in geographical analysis through various cases.The results show that the proposed methods could be applied in geographical analysis for different kinds of different research objectives. |
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