Spatiotemporal characterization of megaregional poly-centrality: Evidence for new urban hypotheses and implications for polycentric policies

Poly-centrality is an essential feature of megaregions and is generally considered an important source of megaregional vitality and competitiveness. Numerous studies have highlighted the growing trends of poly-centrality across different megaregions worldwide. However, with accelerated urbanization, some observations suggest that the existing polycentric urban theories must be improved and that decision-makers require more knowledge on the potential trends, spatial characteristics and influencing factors of polycentric development to implement sustainable regional governance under this context. This paper proposes a series of hypotheses on spatiotemporal dynamics of polycentric megaregion evolution and verifies them in an empirical study on the Megaregion around Hangzhou Bay (MAHB). A new algorithm, which is applicable for long time series data, is proposed to evaluate and monitor the status of polycentric development in MAHB. In particular, landscape metrics and average nearest neighbor analysis are employed in the first stage of our algorithm which is designed to implement data compression. Then, the gravity model, minimum spanning tree (MST) and weighed betweenness centrality indicator form the second stage which aims to construct and explore the polycentric megaregional network. Results show that: (1) the speed and patterns of built-up land expansion significantly affect the number and distribution of megaregion centers; (2) the value of poly-centrality reaches a maximum in approximately 2013 and then declines, which can be well fitted by a Gaussian curve; and (3) the variation of poly-centrality is successively dominated by an increase and decrease in the number of centers with urbanization. This paper renews the assumptions in current polycentric evolution models and provides evidences for single-peaked change of megaregion center number instead of “wave-like”, “scaling-up” or monotonous change proposed in existing urban theories. The proposed algorithm and assumed mechanisms can also be applied to model and explore poly-centrality dynamics of other megaregions around the world. The results are believed to provide critical implications for polycentric policies.