Abstract
Informal patterns of spatial division often persist in historically divided societies where segregation has been officially dismantled. This paper presents a theoretical model to explain why, focusing on the desegregation-resegregation dynamic. The Boundary Transgression Model highlights two interconnected pathways - social psychological and human geographic - that shape intergroup relations under conditions of change, fostering the re-emergence of distance, division, and contact avoidance. It frames resistance to desegregation as a response to constructions of boundary transgression, "ruptures" to the socio-spatial order. The argument is developed through a 25-year research programme in post-apartheid South Africa and post-accord Northern Ireland. The paper also proposes an expanded integration strategy, complementing the prejudice reduction model of change in social psychology. This aims to transform not only person-person but also person-place relations, bringing social psychologists into dialogue with environmental psychology, geography, and urban sociology, and with practitioners in urban design, public policy, and architecture.