Delineating hierarchical activity space from high-resolution urban mobility flows

TL;DR

This paper introduces the Hierarchical Activity Region Model (HARM) to better understand urban mobility hierarchies from relational spatial interactions, demonstrating its validity through taxi data analysis in NYC before, during, and after Hurricane Sandy.

Contribution

The study presents a novel hierarchical activity space model based on relational space, capturing the hierarchical properties of human mobility overlooked by traditional absolute space models.

Findings

Urban travel retains hierarchical organization during disruptions.

Travel hierarchies compress and rebound after major weather events.

Heterogeneity in mobility hierarchies relates to population profiles.

Abstract

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.