Intercity mobility reveals the hyperbolic geometry of city systems
This work addresses the interplay of hierarchy and proximity in urban systems, which is crucial for spatial planning and regional policymaking, though it appears incremental in applying hyperbolic geometry to a known domain.
The authors tackled the problem of understanding how hierarchy and proximity shape intercity mobility and city systems by developing a geometric model based on hyperbolic geometry, which was validated against 12 nationwide datasets and revealed non-stationary city-hinterland relations.
The hierarchy and proximity are key dimensions of urban relational processes, but their interplay in shaping intercity interactions and the underlying structures of city systems remain unclear. We develop a novel geometric model of city systems embedding intercity mobility into a latent hyperbolic geometry, which unravels the measures of hierarchy and proximity accounting for their interplay. It is successfully validated against 12 different nationwide intercity mobility datasets. We find a bottom-up emergence of city hierarchies, along which the variations of city-hinterland relations are non-stationary in terms of their nesting and range properties. Such non-stationarity originates from trade-offs between city hierarchy and hinterland range in determining the formation of city-hinterland structures. Hierarchy- and proximity-dominated urban processes can be elucidated from examining dynamics of the trade-offs. The revealed urban relational processes of city systems are at the core of the emerging science of cities and crucial for spatial planning and regional policymaking.