Information technology plays a growing role in planning procedures. A procedure step which has not been supported by specific computer tools up to now, is asynchronous discussions. Such discussions can occur in public participation as well as between planners during plan design. In this paper I introduce argumentation models as a way of structuring debates, and review existing tools for recording argumentation. A limited number of tools support design-related or map-related discussions. Their short-comings for analyzing geographically referenced arguments are discussed. Finally, the concept of `argumentation maps' is described, which combine the strengths of rigorous argumentation modeling and detailed geographic location to support map-based discussions in on-line planning.