There is a persistent sense that modern urban development lacks some of the intricate functional complexity of more traditional urbanism. And while new urbanisations tend to adapt and develop new elements and functionalities becoming more complex over time, many later urban expansions seem to remain differentiated for longer, contrasting with the traditional city. This is especially perceived in sprawled and suburban environments. Yet the way to approach this keeps focusing on issues of density or an allegedly segregated location in the latter, while potential structural discrepancies receive scant attention. In this study, we argue that a structural variation resulting in a dislocation lays behind the peri-urban difference observed in rapidly expanding cities, looking to give new perspectives on the debate of urban growth and the potential impacts on the traditional city. We are then distinguishing dislocations coming from later rapid urban expansions from the standard discontinuities found within the urban structure. We use urban morphology and complexity science methods such as percolation analysis to give new insights into its understanding. Two study cases are use to analyse this phenomenon: the city of Valdivia, in Southern Chile, and Boston, Massachusetts, USA. The results uncover different forms of dislocations in the peri-urban development of these traditional cities at a structural level, which seems to connect with a change in planning towards the patterns of mass-produced organisation.