This paper describes the conception, development and deployment of a novel HCI system for public participation and decision making. This system was applied for the process of allocating refugee accommodation in the City of Hamburg within the FindingPlaces project in 2016. The CityScope a rapid prototyping platform for urban planning and decision making offered a technical solution which was complemented by a workshop process to facilitate effective interaction of multiple participants and stakeholder groups. This paper presents the origins of CS and the evolution of the tangible user interface approach to urban planning and public participation. It further outlines technical features of the system, including custom hardware and software in use, utilization in real time as well as technical constraints and limitations. Special focus is on the adaptation of the CS technology to the specific demands of Hamburg FP project, whose procedures, processes, and results are reflected. The final section analyzes success factors as well as shortcomings of the approach, and indicates further R&D as well as application scenarios for the CS.