Current public policies request to urban planners to build cities on themselves, decreasing their ecological footprint and energy demand, without compromising citizen health and comfort. Recent climate change mitigation and adaptation issues represent a serious opportunity to point out local climate characteristics and impacts, and take them into account in a global urban planning strategy. This work is dealing with urban heat island (UHI) effect, which is supposed to be more prominent as heat waves may increase in frequency and intensity during the next century. The impact of the city on the climate, and vice versa, were deeply investigated by the scientific community for more than thirty years, and led to the development of various exhaustive physics-based simulation models. They could constitute helpful tools to obtain quantitative data, but a majority of practitioners do not have the technical background and enough time to run these models and analyze their complicated outputs. DIACLIMAP project (2015-2017) aimed to develop an urban climate – i.e. UHI effect – diagnosis tool, based on an empirical approach linking climatic indicators (derivated from air temperature observations during nocturnal cooling periods) and urban patterns indicators (related to the internal district layout and land use, actually based on Local Climate Zones (LCZ) scheme) in a GIS environment. The project consortium worked to optimize methods for a systematic generation of the relevant input and output indicators. The general approach has been developed and applied to an French mid-latitude city (Nancy) and it will be adjusted and validated on two other French mid-size conurbation for the next steps. Some methods have also been proposed to produce vulnerability maps, based on spatial cross analysis of the previous climatic indicators and thematic data as building construction quality or socio-demographic exposition classes. The results showed that different “priority” areas could be identified regarding the choices of the vulnerability multiple criteria and related threshold that could be flexible. To go further this decision making support questions, the specificity of the project was to adapt the tool, firstly regarding the actual regulatory frameworks for French urban planning, but also by retro-actions during its development, according to the awareness and expectations of various city technical services. The process relied on co-design workshops that involved after their identification, different concerned stakeholders (e.g.: users, policy-makers and technicians, urban-planners, urban climate experts, etc.). By mobilizing a shared knowledge, the cross-expertise (technical, usage, etc.) – basics of collaborative engineering – and opinion on potential levers to integrate these issues in planning, we were able to collect suggestions that served the design of a web mapping demo application, that is a first version our proposed operational tool