De‐Densification and Decoupling Trends in the Relationship Between Population and Built‐Up Areas: A <scp>GIS</scp> Model Beyond Administrative Boundaries (Spain, 1975–2020)

ABSTRACT Space–time demographic and built‐up trends are crucial in the European challenge of socio‐territorial cohesion and the Urban Agenda. This research aims to analyze the space–time patterns of population and built‐up areas in Spain between 1975 and 2020, without the constraints imposed by administrative boundaries. To this end, we used the freely available Global Human Settlement Layer to analyze 3D bins and emerging hot spots for population and built‐up areas. Our results showed that the space–time patterns for built‐up areas are more homogeneous than those for population, reducing built‐up cluster diversity to two cold‐spot types and four hotspot classes. In contrast, population dynamics exhibit greater variability, encompassing all eight possible hotspot categories and seven distinct cold‐spot types. The 37.46% of the surface area corresponds to both built‐up and population cold trends. Conversely, 11.91% of the surface area encompasses both hot spots coinciding with functional urban areas (FUA) and extending beyond their boundaries, where 74.93% of the population resides. Surrounding FUA areas exhibit decoupling trends, with dynamic built‐up patterns and static or declining populations. Furthermore, dynamic areas showed declining density as the effective density decreased by 26.87%. The method can be transferred to other countries, and the insightful results could assist policymakers.