Quantifying Administrative and Functional Border Effects on Commuting and Non-Commuting Flows: A Case Study of the Shanghai-Suzhou-Jiaxing Area

As cities continuously expand and with the advancement of regional integration, the flows of people, goods, and information have spread beyond their original administrative borders. The top-down administrative borders and bottom-up functional borders divide city regions into areas with different attributes and hierarchical structures. Although existing studies have quantified border effects from the perspective of spatial interaction, these have not clarified the differentiated effects between administrative and functional borders on different flows of activities. Without considering the original administrative borders, this study first proposed a fine-grained spatial unit clustering method based on spatial interaction networks of commuting and non-commuting flows to delineate functional borders. Then, the administrative and functional border effects are evaluated through the gravity model, revealing their influence on travel flows of the city region. This study takes the case study of a mega-city region, the Shanghai-Suzhou-Jiaxing (SSJ) area in China, using mobile phone data. The results indicate that the commuting and non-commuting networks in the SSJ area exhibit a cross-border polycentric hierarchical spatial structure. Both administrative and functional borders have significant effects on spatial interactions, but compared to commuting flows, non-commuting flows are more sensitive with functional borders. Provincial borders exert the most prominent positive effect and exhibit spatial heterogeneity. Meanwhile, the results of border effects might be utilized by policymakers to focus more on promoting the spatial integration of cross-border regions within the SSJ area.