## 6 Conclusions  
This study was conceived as the first step toward the further implementation of the 3D modelling approach. A better correlation between the UES and z-value must be tested, in order to explore the complexity of the urban spatial configuration and to improve the results of consequent decision-making processes. The SDMSS incorporates 3D modelling as a central component. The third dimension included in the UES assessment identifies a relevant opportunity to understand the details of urban structure-function relationships, improving modelling and the visualisation of data and related impacts. The proposed methodological framework supports the evaluation, planning, and monitoring of UES within a 3D virtual environment, overcoming the limits of 2D representation and helping decision-makers to localise, assess, and manage urban development strategies. The SDMSS addresses one of the main challenges in sustainability research related to the elaboration of spatial models, adapting to changes in managing sustainable transformations. The 3D virtual environment supports the representation of multiple services at the same location within a unique map, even if it does not enable the description of changes in services over time at present. The 3D modelling, conceived as an integral part of web-GIS, could allow for the inclusion of the time dimension and the visualisation of changes and transformations dynamically. At the same time, 3D modelling in a virtual environment allowed us to represent relationships between z-elevation values and specific UES spatially, highlighting the system of relationships between the heights of the buildings and the quality of services that each cell features. One of the significant contributions offered by the SDMSS is the possibility of visualising UES trade-offs simultaneously, in order to identify opportunities linked to a sustainable spatial policy where economic, ecological, and social components should reach a balance. Another result of applying the proposed model is the possibility to implement a multi-scale decision-making process, where the scale of analysis and assessment influences the problem definition and the related results, including different interests with respect to the issues addressed for each scale. The synthesis maps for each function--related to Regulation, Carrier, and Information services implemented with the aggregation rule of the spatial AHP--can be used to produce a normalised index of UES per cell. This index is the expression of a multi-scale assessment, incorporating different dimensions that are not present in single-scale assessments, including the selection and quantification of UES. The spatial AHP method for aggregating (or even downscaling) to support comparison across scales establishes a mechanism for ensuring information flow across the scales of the assessment and integrating them. The multi-scale approach also tries to address the challenge related to stakeholder involvement and participation, adopting a more flexible process, as necessary to include different scales (i.e., political, economic, social, cultural, and environmental). The AHP multi-criteria aggregation process was used for mapping the distribution of UES for each function, combining visual and non-visual information of the MMU. The results of the applied approach can support the elaboration of planning scenarios, considering the degree of suitability per MMU related to the selected UES. Future developments of this research aim to stress some of the opportunities identified, such as including other cultural and social services, which are crucial for analysing and understanding urban dynamics. In this framework, one of the main challenges in sustainability research is to conceive models that are capable of adapting to changes in scale and recalibrating the selected indicators, depending on the degree of detail and data availability.