Digital tools are being developed for involving stakeholders in urban planning and transformation processes. One challenge is how to visualize and act upon all parameters that are relevant for dealing with complex plan-ning problems, such as environmental factors. Dialogue tools involving vis-ualization can bridge the distance between planners and citizens. This paper focuses on the problem of representing invisible environmental parameters affecting the urban climate such as wind, solar radiation, air pollution and noise, in a city model. The aim of the paper is to discuss challenges for rep-resenting and communicating environmental data in city models. In this pa-per, we have accounted for literature studies; our own conceptual modelling and prototype studies in three projects; as well as a survey with 16 urban planners. We conclude with defining design criteria for dialogue tools cre-ating a comprehensible base for communication in urban transformation processes.