Taking provinces as the flow nodes, this paper examines the spatial evolution of China's crude oil flow in five typical years selected from the research period 1985-2009. According to the oil self-sufficiency ratio and liquidity ratio, flow nodes are divided into three types: source regions, sink regions and transit regions in five typical years, respectively. Then, adopting the gravity center and standard deviational ellipse, this paper analyzes the central tendency and dispersion pattern of the spatial distribution of the sources and sinks, in order to clarify the spatial displacement and shape change of source-sink system. Some conclusions can be drawn as follows.
(1) Although mainly located in the northeast of China, the gravity center of source system of crude oil flow had moved northwest from 1985 to 1995, and then southwest from 1995 to 2009. As a whole, its moving speed in the north-south direction was higher than that in the east-west direction. The gravity center of sink system of crude oil flow was mainly located in east China, its moving ranges were relatively small compared to the source system, and it mainly moved in the north-south direction from 1985 to 1999, while mainly in the east-west direction from 1999 to 2003, and lastly inclined southwest.
(2) The analysis of standard deviational ellipses shows that the spatial pattern of source system became centralized in 2003-2009 after decentralized in 1985-1999, and its dominant distribution direction had changed from northeast-southwest to approximate northwest-southeast. The distribution pattern of sink system was relatively stable, which became slightly centralized in 1985-2003, and then somewhat decentralized, and its dominant distribution direction has always maintained as northeast-southwest.
(3) As expressed by the evolution of the link between the gravity centers of source system and sink system, the mean direction of crude oil flow in China had gradually changed to north-south from northeast-southwest, and the mean flow length tended to decline. As shown by the evolution of the links between the principal axes of source system and sink system, the dominant direction of crude oil flow in China gradually changed from northeast-southwest to northwest-southeast and east-west.
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