Sadegh Saeidishirvan, Hashem Dadashpoor, Mojtaba Rafieian
This study challenges the conventional assumption that polycentric urban development inherently reduces spatial inequalities. Focusing on the Tehran Metropolitan Region between 2010 and 2020, it demonstrates that housing affordability crises can actively generate—rather than mitigate—polycentric structures. Using satellite-derived built-up data (GHSL) and 572,198 housing transactions, the analysis reveals a marked increase in morphological polycentricity, as indicated by a flattening of the rank-size slope (from −1.558–1.343). Simultaneously, core urban areas experienced severe erosion in affordability, with the purchasing power of median-income households declining by 40–59 % in premium districts. This affordability pressure drove disproportionate peripheral expansion, with low-cost counties experiencing an average built-up growth of 76 %, compared to just 4.8 % in the high-priced Tehran. A spatial threshold analysis (5 m²/year of purchasing power) shows a sharp contraction in affordable zones—from 19 to 9 districts—tracing a center-to-periphery displacement pattern. Notably, Tehran and Shemiranat emerge as a continuous exclusionary zone, replicating inequality dynamics across administrative boundaries. These findings invert prevailing policy orthodoxy by showing that polycentricity can result from spatial exclusion, rather than serving as a corrective to it. Without coordinated measures to preserve affordability, decentralized urban growth may deepen—rather than resolve—spatial inequities. The study offers important implications for Global South megacities grappling with similar affordability crises and fragmented regional governance.