This contribution focuses on the Strategic Environmental Assessment (SEA) as an important tool to ensure sustainable development and reach a high level of environmental protection. More specifically, this paper provides an evaluation method based on the integration of Geographic Information System (GIS) and Multi-criteria Analysis-named Integrated Spatial Multi-criteria Decision Support System (ISMDSS)-to support the preparation of environmental assessment reports and the construction of scenarios for the adoption of urban plans, as an innovative tool that integrates objectives and multidimensional (economic, environmental, and social) components, as well as different approaches and models for the construction of a long-term shared vision. In particular, considerations are made by presenting a thought-provoking case study on the SEA of the urban plan of the municipality of Marzano di Nola, located in the province of Avellino in the Campania region. The experiment carried out showed the potentiality of the ISMDSS to evaluate the impacts of different scenarios with the aim of developing a sustainable urban municipal plan. The spatial dimension is useful in understanding the dynamics that characterize each environmental topic in a specific area, by considering not only the components of the natural and developed environment, but also the interactions with social and economic components.