One cannot conduct such studies on real cities except, perhaps, as a point of departure at some specific point in time to provide an initial layout for a city knowing that future forms derived by the studies will diverge from that recorded in history. An entirely imaginary city is therefore chosen. Although the components of this city at the level of individual buildings are taken from known cities in history, this choice does not preclude alternative forms of the city. To some degree, building types are invariants and, as argued in the Appendix, so are the urban typologies into which they may be grouped. In this imaginary city students of urban history play the role of citizens or groups of citizens. As they defend their interests and make concessions, while interacting with each other in their respective roles, they determine the nature of the city as it evolves through the major periods of Western urban history in the form of threedimensional computer models.

My colleague R.J. van Pelt and I presented this approach to the study of urban history previously at ACADIA (Seebohm and van Pelt 1990). Yet we did not pay sufficient attention to the manner in which such urban models should be structured and how the efforts of the participants should be coordinated. In the following sections I therefore review what the requirements are for three-dimensional modeling to support studies in urban history as outlined both from the viewpoint of file structure of the models and other viewpoints which have bearing on this structure. Three alternative software schemes of progressively increasing complexity are then discussed with regard to their ability to satisfy these requirements. This comparative study of software alternatives and their corresponding file structures justifies the present choice of structure in relation to the simpler and better known generic alternatives which do not have the necessary flexibility for structuring the urban model. Such flexibility means, of course, that in the first instance the modeling software is more timeconsuming to learn than a simple point and click package in accord with the now established axiom that ease of learning software tools is inversely related to the functional power of the tools. (Smith 1987).

How is the research situation? Using several standard research data banks, the author collected articles and book(chapter)s on architectural psychology in German- and English-language countries from 1990 to 1996. Studies on main architecture-psychology interface problems such as user needs, housing quality evaluations, participatory planning and spatial simulation / virtual reality did not outline an “old, settled” discipline, but rather the sketchy, random surface of a field “always starting anew”. E.g., discussions at the 1995 EAEA-Conference showed that several architectural simulation studies since 1973 caused no major impact on planner's opinions (Keul&Martens, 1996). “Re-inventions of the wheel” are caused by a lack of meetings (except this one!) and of interdisciplinary infrastructure in German-language countries (contrary to Sweden or the United States). Social pressures building up on architecture nowadays by inter-European competition, budget cuts and citizen activities for informed consent in most urban projects are a new challenge for planners to cooperate efficiently with social scientists. At Salzburg, the author currently manages the Corporate Design-process for the Chamber of Architecture, Division for Upper Austria and Salzburg. A “working group for architectural psychology” (Keul-Martens-Maderthaner) has been active since 1994.