Citizen participation (CP) is at the heart of many discourses today, but is struggling to establish itself in public institutions. In the case of urban design (UD), encouraging initiatives can be observed. Nevertheless, observations also lead to the observation that the methodologies currently used are mostly based on artisanal tools. This thesis focuses on the integration of digital tools in the process of citizen participation in the design of public spaces. More specifically, the work is focused on a collaborative mode of consultation applying the concepts of co-design, which aims to bring together citizens and urban design professionals in the same place, to build a common language and a shared vision. Through a research methodology based on design science, this transdisciplinary research considers both the context of application, and theories in the field of digital CP and co-design. Indeed, it is pointed out that existing research works are either too theoretical in the field of CP and do not propose the instantiation and the evaluation of an artifact through a prototype, or too much centered on the technology while leaving aside the context of application. Moreover, in order to fill a gap in the current state of the art, a particular emphasis is put on improving the creative expression capabilities of citizens through co-design, and the realization of an intuitive interface dedicated to amateurs.