Contiguity without continuity. Approaching urban fragmentation through boundaries

Urban fragmentation as a process of spatial differentiation is increasingly shaped by the internal boundaries and discontinuities that segregate identified parts of the metropolitan areas from within. This article challenges the treatment of cities and metropolitan areas as unified entities, proposing instead that the spatial pattern of urban fragments might reveal how the differentiation processes operate by transcending conventional administrative units. To capture this complexity, a methodological framework has been developed, focused on the detection of discontinuities within and between census tract boundaries, integrating socioeconomic, morphological, and housing dimensions into a unified analytical approach. The analysis draws on census microdata and cadastral dwelling-level data covering over 3,200 census tracts, processed through a GIS-based boundary detection workflow, principal component analysis, and k-means clustering. The resulting typology of boundaries and potential urban borders reveals differentiated fragmentation patterns between the city core and the metropolitan rings at a fine spatial scale. These findings show that mapping and measuring internal urban discontinuities offers a richer and wider understanding of urban fragmentation and how socioeconomic inequalities are inscribed in the built environment.