Who moves where—and what housing choices do they make? uncovering spatial polarization through life-course migration in a shrinking megacity

Spatial polarization is a bottom-up process embedded in life-course trajectories rather than arising solely from macro-scale demographic decline. This study examines how life-course migration and housing choices shape spatial polarization in the Tokyo Metropolitan Area (TMA), a prototypical shrinking megacity. Using an integrated framework—combining survivorship-based cohort estimation, robust multiple linear regression, random forests, and geographically weighted regression—this research links micro-level residential decisions to broader demographic and structural transformations. Results identify three life-course migration cohorts whose divergent housing choices reinforce a polarized geography of youthful cores, family-oriented inner suburbs, and ageing peripheries. Young adults cluster in central Tokyo’s high-density rentals near transit hubs; young families pursue homeownership and educational access in western Tokyo and inner suburbs; while older seniors relocate to eastern Tokyo and peripheral municipalities, shaped by low-cost rentals and rural attachments. Across cohorts, housing tenure emerges as the strongest determinant of Migration Pattern Intensity (MPI), outweighing land prices, neighborhood characteristic, and accessibility. These findings advance the concept of a “polarized life-course housing trajectory” to explain how housing choices across life stages accumulate into multiscale polarization, intensified by intergenerational transfers. The study introduces this novel lens to bridge macro-structural shrinkage with micro-level residential practices to understand spatial polarization. Policy insights stress integrating foreign labor and multicultural inclusion at the regional scale and promoting multi-generational housing locally to mitigate suburban shrinkage and ageing. These strategies resonate with the SDGs and global sustainability agendas, offering lessons for urban governance in megacities confronting demographic contraction. • Uncover spatial-polarization mechanisms in a shrinking megacity through an ordinary life-course migration perspective. • Introduce Migration Pattern Intensity (MPI) to capture multiscale heterogeneity across life-course groups. • Highlight Tokyo's polycentric structure challenge of “Youthful urban centers, Favored inner suburbs, Aging periphery” • Reveals housing tenure as the strongest determinant of migration intensity across life stages. • Propose a “polarized life-course housing trajectory” driving intergenerational inequality.