SIMULATION TOOLS FOR THE DYNAMIC EVOLUTION OF TOWN SHAPE PLANNING
The experimental research I have recently been doing springs from a question. It is possible, with custom designed software, to simulate the dynamic morphological variation of the urban image? And to simulate the development through time of formal town evolution, time that is taken by irreversible architectural events and that renders the urban landscape increasingly complex? Yes, if we try to work directly with the instability of dynamic town systems, and decline to base our analysis on the equilibrated moments that represent only (when they occur) an accidental configuration in town time development. This is a morphological approach that identifies the "modus operandi" of formal transformations during the time, and using algorithms, writes the rules of the dynamic and chaotic system that draws the town image development. This scenario of possible town development is made up of an infinite number of unexpected and dissimilar images. Each image springs from an iterative process of formalisation which, ad each stage, increases the complexity and randomness of the result. The paper I propose, accompanied by images of scenarios of possible town environments generated by my software (examples include medieval, technological and contemporary metropolitan environments) explains and demonstrate this research and its possible application in urban planning. I have published this research in my book: Celestino Soddu, "Citta' Aleatorie" Masson Editor, Milano 1989. INTRODUCTION The possibility of computer simulation of the dynamics of system evolution achieved recently in many scientific fields has given a new stimulus to research. Computer simulation applied to town planning modifies the traditional approach to this discipline: experience and causal explanation. The problem of interchangeability of reality with a formalised system, of passage from determinism to formal logic is still open. This paper is on the experimental utilisation of formal logic for the simulation of urban shape development. The software I present was developed, starting with the disequilibrium state of the system (the presence of different architectural forms together with different stages of urban growth, often contradictory) to simulate time and produce a series of computerised three dimensional models of urban shapes, identifiable as a whole as "species" and differentiated as "individuals" These models represent the multiplicity of possible scenarios of a town after a simulated evolution. THE SIMULATION OF A TOWN SYSTEM The development of adequate control and representation tools is necessary for a systematic approach to the contemporary ever changing urban shape in order to evaluate the morphogenetic dynamics, the structure of the history of towns, that is stressed by the architectural events, that are not reversible and modifies the development of urban growth. The displays currently used have an incontestable limit that is the difficulty of examining one of the most important aspects of urban shape: time. A display that is approximate with respect to time dynamism, that is limited in tracing and controlling urban shape referring only to the stationary moment of hypothetical equilibrium, denies the essence of the town. It is an abstraction where urban time is absent, frozen into a reductive representation of successive moments of equilibrium. Towns are, in fact, accumulations of events with different and often contradictory objectives; their structures are unstable, their evolution unpredictable. Instruments, capable of examining and testing the dynamics of transformation render possible a positive approach towards the comprehension of urban structures. the target is to operate into the morphogenetic dynamics and not only into the occasional modifications. If the purpose of graphic representation is to investigate urban patterns and their progressive disintegration and/or requalification, the instrument used should trace back and analyse the formation process of urban shape through simulation of the entire cycle. Every architectural event does, in fact, modify urban shape as every urban shape modifies successive architectural events. If we try to investigate on the cycle architecture/town evaluating the causes and events that have determined every formal order, we will be in the impossibility to continue our work. Every formal architectural detail is the product of a variety of causes belonging to different spheres: cultural, technological, economical and functional including subjective and casual aspects. Even if we leave out the casualness of some choices, we will not be able to attain, with sufficient approximation, a scenario susceptible of verification. This is due to the fact, that, to arrive at a cause and effect relationship, it is necessary to analyse every cause. It means, for a town system in its formal evolution, to analyse and evaluate every event, from urban and economical choices to an unknown master builder who, centuries ago, changed the original project, from political choices to carelessness that has caused the collapse of a building. The awareness of the impossibility of evaluating all the causes that brought about the actual urban shape should bring us to operate within a specific field based on form and its transformation in order to obtain more exact and pertinent results. This implies the capacity of identifying a logical process to explain how and not why a form is evolving, how and not why an aggregation of forms gives a recognisable urban shape. The results did within a specific field, using a multidisciplinary approach transferred in the same formal logic, are more pertinent, verifiable and available for utilisation in real situations. It is possible to have a direct approach to a town formal dynamism and to follow its transformation using adequate algorithms. It is not useful, for example, to analyse systematically all the causes that brought about a town expansion in order to give a model. It is less dispersing and reductive to define the transformations that have taken place using an algorithm. This algorithm will produce, on request, the successive contour lines of the town expansion based on preexisting formal elements like traffic arteries, soil morphology, relations with nearby towns and villages..etc. This algorithm will be unveiled and identified inside the dynamics of successive transformations without considering external causes and will always produce different urban contour lines. Its correspondence to reality will be calibrated by means of subsequent verifications done on a sufficiently large number of results. The algorithm should be adopted only when all simulated transformations, in their evolution are congruent with a specific "species" of urban configuration. Every configuration, although produced randomly and unpredictably, should be identifiable as part of an entity that can be found in reality. The same approach is used for the transformation of a square. An algorithm, capable of representing possible transformations between buildings and open space can be traced in order to generate different architectural solutions having the same size and form requisites and respecting the characteristics of the square. This approach, which is exclusively morphological, allows reproducing the complexity of urban shape in its morphogenetic dynamism. However, can this be used in reality? Can it become an operative tool for the control of growth and evolution of the cities we live in? Like all mathematical and formal models, those that represent the logic of urban evolution are an effective tool to simulate interactions. Any variations in the model generate transformations that can be analysed and evaluated in relation to time. Each result is identifiable and characteristic and always reflects the identity of a single town. Each result is like an "individual" and each series of results like a "species" To represent the "species" instead of the "individual" offers many advantages. First of all, it allows us to evaluate to what degree a few and limited changes can interfere, after a simulated time, in urban shape through the infinite series of transformations produced. It can also help us to identify the phase in which our model produces transformations such as to bring about the loss of a town identity. What are the characteristics of a formal transformation of a town system and how can it be represented and simulated? RANDOMNESS AND EVOLUTION, INSTABILITY AND TIME As clouds, towns evolve with time, expanding, contracting, transforming themselves, their image, their characteristics under economical, cultural, political and technological impulses. It is easy to predict, in short terms, the development of towns, as for any natural system. Everything happens according to precise rules deriving from urban planning, current technology, economic and social influences. However, previsions are almost impossible in long terms since towns are inhabited by man and that each choice, each successive step brings about margins of subjectivity and unpredictability. This subjectivity produces one of the most important characteristics of urban shape: formal diversity of solutions responding to the same necessity. It must be remembered that most subjective and casual aspects of decision making have little influence and will disappear in the subsequent transformations of a town. However, some events or marginal aspects will persist and, because of concomitant casual circumstances, they will assume more and more a capacity of influencing the course of future development. This influence, once it has been consolidated becomes irreversible and can outgrow the importance of the event that caused it. Some architectural forms, originating from the contingent, casual or subjective choices very often loose their raison d'etre and become pure formalisation of relations between following events; they often disappear surviving only as