image: Inter-city travel volume and travel distance distribution view more
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Megacity region is an advanced form of human urban settlement. Inter-city mobility plays an important role in megacity regions’ sustainable development. Although gravity model has been proved to be an effective model for characterizing inter-city mobility and widely used to predict traffic flow, most of the existing studies are based on traditional survey data, and the research conclusions are limited to to overall population mobility, while the difference in inter-city travel with different purposes is unexplored on such a large geographic scale. The research published in SCIENCE CHINA Earth Sciences by Pengjun Zhao, Haoyu Hu, Liangen Zeng, et al. revealed the hierarchical structure of inter-city mobility in megacity region, verified and optimized the gravity model of inter-city mobility, and calculated the difference of gravity model parameters for different travel purposes for the first time using mobile phone trajectory big data in Jing-Jin-Ji, China.
Megacity region is a highly-developed form of urban space, which is a dense, urbanized region with multiple sizes of cities, proximately located and functional networked, clustered around one or two large cities Inter-city mobility in megacity regions is different from that in other regions in that boundaries between urban and rural areas tend to be blurred and that socioeconomic ties of various types are more complex and intertwined. Gravity model is a mathematical model to reveal the interaction law of geographical space. In view of the shortcomings of existing studies in terms of research scale, regularity differences of different travel purposes and research data, this study focuses on three issues. First, what are the differences between inter-city commuting and inter-city non-commuting travel behaviours in the megacity region? Second, does the volume of inter-city mobility have a typical hierarchical structure? Third, what determines the distribution of inter-city mobility in the megacity region?
The study found that non-commuting is the main purpose of inter-city mobility. Inter-city trips are mainly concentrated in the region’s central area around the biggest city (Figure 1). The inter-city travel distance of different travel purposes varies greatly. The distance of commuting is the shortest. People are willing to travel longer distances between cities for non-commuting purposes. On the whole, there is a positive correlation between travel distance and city size. For cities in which the employed population is greater than the residential population, inter-city travel distance tends to increase significantly with the expansion of city size. For cities in which the residential population is greater than the employment population, the inter city travel distance varies and there is no obvious correlation with the city size.
There is a hierarchical structure rule of inter-city mobility, namely, the distribution of both the city size and its travel volume follows Zipf’s law. It is found that the Zipf curve of travel volume is much steeper than that of the general population. This result shows that compared with the prominent difference in population size of these major cities, their difference in inter-city travel volume is smaller. The inter-city commuting hierarchy is more concentrated than that of non-commuting travel behaviours (Figure 2). Specifically, large cities’ advantages over small cities in inter-city commuting travel volume is greater than that in inter-city non-commuting travel volume.
It is found that a hybrid model integrating both population and job-housing balance variable is more efficient than a model that only includes population or GDP, since the hybrid model can give a more accurate travel volume prediction. Commuting and non-commuting inter-city trips suit different gravity models. The best indicator for the attraction of inter-city commuting is GDP, while the best indicator for attraction of inter-city non-commuting is population. In non-commuting, the attraction of home-based travel is a better representation residential population, while that of non-home-based travel is indicated more accurately by employed population. Job-housing balance is a significant indicator for home-based travel, both commuting and non-commuting, while it is not a significant indicator for non-home-based travel. In home-based travel, job-housing balance has greater impact on commuting than on non-commuting. The optimized gravity models produce effective prediction results (Figure 3).
The findings contribute to new knowledge on basic inter-city mobility laws, and they have significant applications for regional policies on human mobility. For more details, please refer to the upcoming paper "Revisiting the gravity laws of inter-city mobility in megacity regions", to be published in SCIENCE CHINA Earth Sciences: https://link.springer.com/article/10.1007/s11430-022-1022-9
Zhao P, Hu H, Zeng L, Chen J, Ye X. 2023. Revisiting the gravity laws of inter-city mobility in megacity regions. Science China Earth Sciences, vol. 66, No.2, https://doi.org/10.1007/s11430-022-1022-9
Journal
Science China Earth Sciences