Public governance reliance on digital platforms increasingly raises new questions regarding the transformation of local governments and their capacity to engage in platform-based ecosystems. This study aims to map and assess the level of platformization in the 308 Portuguese municipalities through the development of a composite indicator - the Municipal Platformization Index (MPI). Building on the literature on e-government and digital transformation, platformization is conceptualised as a multidimensional and evolutionary process, encompassing not only advanced digital architectures but also the infrastructural and organisational conditions that enable them.

Data was collected from a national survey of Portuguese municipalities and structured into five analytical dimensions: 1) technological infrastructure, 2) digital services, 3) cybersecurity, 4) digital capacity and planning, and 5) citizen interaction. Within each dimension, a set of Key Performance Indicators (KPIs) was defined and standardised, using Principal Component Analysis (PCA) to derive objective weights for the indicators. MPI was computed as a weighted composite index, enabling the comparison of municipalities across different contexts.

Results show territorial cleavages between high-density and low-density municipalities, with the former generally achieving higher levels of platformization. However, the analysis also showed that some municipalities perform above (overachievers) or below (underachievers) their expected levels given their contextual characteristics, suggesting that dimensions alone do not fully explain variations in municipal platformization levels. This study contributes to the emerging discussion on the use of digital platforms in the public sector, providing empirically grounded framework for analysing digital transformation at the municipal level, replicable across different European counterparts.