Delineating hierarchical activity space from high-resolution urban mobility flows
This work addresses urban planning challenges by providing insights into mobility hierarchies for more sustainable and resilient cities, though it is incremental in refining existing relational space concepts.
The study tackled the problem of modeling hierarchical activity spaces in urban mobility by proposing the Hierarchical Activity Region Model (HARM), which revealed that intra-urban travel retains hierarchical organization even during disruptions like Hurricane Sandy, with travel undergoing compression effects such as fewer hierarchical levels and enlarged scales followed by a rebound.
Current studies on activity space are limited by the conceptualization of absolute physical space that fails to consider the heterogeneity of relational spaces reconstructed from spatial interactions of human movements between locations and falls short in incorporating the inherent hierarchical property of human mobility. Consequently, these approaches cannot faithfully reflect how people interact with urban spaces through travels. From the lens of relational space, this study proposes the new Hierarchical Activity Region Model (HARM) to derive the space and hierarchical properties of activity spaces perceived by various urban groups. We demonstrate the enhanced validity of our model on travel behavior in Manhattan, New York City, before, during, and after Hurricane Sandy on the basis of taxi data. Empirical results show that intra-urban travel retains clear hierarchical organization, even under disruption of a major weather event. Yet, travel undergoes a compression effect in travel hierarchies, characterized by fewer hierarchical levels and enlarged characteristic scales, followed by a rebound. Clustering the derived hierarchies reveals pronounced heterogeneity that stems from differences in population profiles; some groups sustain deeper structures or recover quickly, while others experience a persistent loss of levels. This study provides valuable insights into the functional hierarchies of urban mobility, which could inform more sustainable, resilient and equitable urban planning. The proposed methodological framework is generic for studying human mobility in broader contexts.