Spatio-temporal growth and urban polycentricity of secondary cities: The case of Khulna, Bangladesh

Urban polycentric development is increasingly relevant for rapidly growing secondary cities, yet empirical evidence from such contexts remains limited. This study explores the spatio-temporal transition of polycentricity of Khulna, a secondary city of Bangladesh, by specifying its historic core and two emerging new centers, thus providing the preliminary evidence of polycentric urban structure. Using advanced spatial analysis techniques, we mapped built-up expansion and quantified urban concentration over 30 years. Results reveal that, while the old city center remains a dominant node, two distinct new centers have emerged, together shaping a pronounced polycentric pattern. Additionally, low Shannon entropy values in the spatial distribution of built-up areas suggest a dispersed but multi-nodal urban form and a significant potential for future densification. The identification of several active centers challenges the conventional monocentric planning approach and highlights the need for policies that find and effectively manage new sub-centers to optimize infrastructure and land use. Additionally, the relationship of entropy with population concentration and transport accessibility jointly explains rising spatial entropy. Future studies should extend this analytical framework to other secondary cities to enable a comparative understanding of such urban growth in rapidly urbanizing areas.