Future computing systems interact with a large number of users moving around buildings and streets. In this paper, we propose an example of such systems and how to evaluate ubicomp systems equipped with a large-scale physical environment that includes a large number of people inside. In our emergency guidance system, off-site guiding staff monitors a crowded large-scale public space to understand its situation, and instruct on-site guiding staff how to guide crowds effectively. Our system tracks and synthesizes the public space to enable the off-site staff to grasp it, and support communication between the on-site and the off-site staffs. Because it is not affordable to use the physical public space and a lot of human subjects to evaluate the system, we used our social interaction platform to simulate our guidance system. We could successfully construct simulations, in which the crowds are replaced with social agents in the virtual public space.