ABSTRACT Metropolitanization represents a pivotal process viewed from various perspectives. It is approached diversely, yet underpinned by a comprehensive understanding of the metropolis and its immediate surroundings’ development. This study introduces a conceptual framework for metropolitanization across four dimensions, distinguishing between qualitative-quantitative and vertical-horizontal delineations. The spectrum of metropolitanization encompasses demographic expansion as well as nuanced qualitative shifts, influenced, for instance, by extensive integration into the global economy and the consolidation of the nation's economic dominance. The proposed framework is applied to three Polish agglomerations, each exhibiting relatively comparable settlement system structures but markedly distinct socio-economic conditions. This approach also assesses the vigour of metropolitanization at varying levels, facilitating the identification of metropolises that, due to their unique challenges relative to other cities, hold strategic importance for developmental policies.