This paper proposes an advanced multi-criteria assessment methodology to develop a Collaborative Spatial Decision Support System (C-SDSS) for spatial planning, focusing on “cultural landscapes” in Italy’s inner areas. The proposed methodological approach underscores the importance of transparent and informed decisions that stem from an understanding of the socio-economic, natural and cultural values of the territory. Underlying the methodological path is the application of Geographic Information Systems and, in particular, the open source platform QGIS, an essential tool for the spatialization, processing and management of quantitative and qualitative data. Indeed, QGIS makes it possible to combine, correlate and analyze different categories of spatial information, accurately describing the distinctive character of the territory in general, and cultural landscapes in particular. The methodological path is divided into three main phases – cognitive, evaluative and restitution – in which GIS allows the collection and organization of heterogeneous data and becomes a fundamental tool for modeling, analysis and communication of results in favor of sustainable spatial planning. This approach takes into account the cultural and landscape specificity of inner areas, helping to enhance local peculiarities and develop a methodology consistent with GRINS – Growing Resilient, Inclusive and Sustainable project aims. Keywords: Inner areas, SOCRATES method, GeoTopsis method, Collaborative decision-making proces.