Worldwide urbanisation emphasises the importance of planning for cities that sustain and promote the well-being of their residents. The planning of a living environment that supports well-being requires both intersectoral cooperation between policy sectors and interaction between researchers and practitioners. With 12 case studies (of 11 Finnish municipalities and one city region), we provide a description of a knowledge co-production process originating from the use of a new planning-support tool called StrateGIS that can be used for discovering built-environment indicators for integrated planning for well-being. Based on spatial multi-criteria analysis, we also investigate how the tool fostered intersectoral discussion among practitioners during the process. Practitioner knowledge was merged with scientific knowledge at different stages of the process: in structuring the value tree, in setting the objectives, in selecting the criteria and in defining the spatial representation for each criterion. Intersectoral discussion during the process was seen as fruitful and relatively easy despite the different types of expertise present in the workshops. Based on our results, the local experts specialised in spatial data have an intermediary role between practitioners since they can build understanding of how data is translated into spatial information when using a spatial planning-support tool.