This paper presents the design of OrMiS, a tabletop application supporting simulation-based training. OrMiS is notable as one of the few practical tabletop applications supporting collaborative analysis, planning and interaction around digital maps. OrMiS was designed using an iterative process involving field observation and testing with domain experts. Our key design insights were that such a process is required to resolve the tension between simplicity and functionality, that information should be displayed close to the point of the user's touch, and that collaboration around maps cannot be adequately solved with a single form of zooming. OrMiS has been evaluated by domain experts and by officer candidates at a military university.