The complexity of the city is increasing due to the impact of recent devcelopments in information and communication technology which is leading to changes in urban development processes, in demographic composition, in cultural and political life. This increasing complexity calls for a new integrative framework for thinking about the development of the cities.

The use of systems view in sociology i.e. in human systems goes back to 1950's and to in planning it is in 1970's. Systems theory suggests that the definition, classification, are needed for understanding and simplification. Forrester's study on Urban Dynamics indicates that, System Dynamics is not merely a technique to provide solutions to provide solutions to specific problems that have been formulated, but it acts as a system methodology which determines the whole style of problem definition, qualitative analysis and change analysis in systems.

This paper presents the case of urban planning as an example of systems thinking and system dynamics in urban and regional planning. It will be argued in this paper to use System Dynamics as a tool in planning rather than accepting all the predicitons of the original Urban Dynamics Model.

Key Words: systems view of planning, urban dynamics, systems philosophy.

SYSTEMS ANALYSIS AND SYSTEMS THEORY

The system is defined as an interacting, and goal directed set of object's taking place in an environment. The city is a system capable of counter intuitive responses which can properly understood and controlled only if the interaction between the basic urban sub-systems are taken into consideration properly. In other words, the main question is not to better understand the individual sub-system (population, service, industry), but to understand how they act together, how they are harmonized into this entity we call a city.

An urban region can be regarded as a complex socio-economic system. The essential characteristics of such a system are that; firstly, they contain a large number of variables, and secondly, many of the variables and sub-systems are connected by feedback relationships. The interconnections.between the sub-systems give rise to the dynamic behaviour of urban systems. The dynamic nature of urban systems also derives from the fact that the feedback relationships operate over time. A basic requirement of a realistic simulation therefore must be ability to incorporate time as a variable in the structure of the model, in order to be able to trace the performance or behaviour of the system through time.

Batty (1980) argues that, the tension between what is possible in systems analysis and what is demanded by a systems approach, has actually sustained the development of a systems theory in planning.

Systems theory suggests that questions of definition, classification, extent and so on are essential prerequisites to understanding; thus, systems theory tends to widen debate about what constitutes the system and problem of interest. In constrast systems analysis and modelling has largely disregarded these questions.

Much more thought should be given to context, factors affecting any problem, to ways of understanding structure and pattern.

Batty (1983) argues that in suggesting broadening of systems analytic thinking according to the original tenets of systems theory, it is essential to consider philosophy.

Concerning the definition and application of systems analysis; it is argued that the major problem in relation to the problem of definiton of "systems analysis" by planners is that the concept refers to the substantive issues such as nature and functioning of cities and regions. Land use modelling in the United States in the fifties and sixties, and in Britain in sixties and early seventies was developed in this context. Breheny (1983) argues that the definiton of systems analysis should also cover procedures or processes adopted in deriving plans i.e. procedural aspects of planning.

The diagram in Figure 1, relates together the ideas of science, which can be assumed concerning with substantive issues, and design which can be equated with procedural, plan making activities, with the notions of theory and practice.

	SCIENCE	DESIGN
THEORY	Substantive issues, knowledge of cities, models, techniques	Theoretical processes, rational decision, model, etc.
PRACTICE	Applied knowledge, practical modelling	Applied processes, practical procedures.

Figure 1.Breheny's (1983) Adaptation after Batty's (1981) Science-Design/Theory-Practice Concept.

SYSTEMS THINKING AND SYSTEMS DYNAMICS

The arguments concerning the concepts of systems thinking, system dynamics and soft OR are presented below.

Kreutzer (1993) argues that there is no "answer" or correct description of reality; what we perceive is interdependent with media and language; focus on processes and dynamic structures; nature of "living systems"; value of model building; design the future rather than predict it. The features of systems dynamics include: structure in social systems is comprised of multiple, interacting feedback loops with time delays and nonlinearities; conceptual modelling methods, simulation to test theories as keys to building substantive knowledge about social systems. Forrester presents the view that systems thinking does not refer to the quantitative and dynamic analysis that constitutes real system dynamics.

It is argued that (Checkland, 1989) soft systems methodology takes "system" to be the name of an epistemological device which can be used to investigate some of the problems in the world and treats what to do as well as how to do it as part of the problem, which means that soft systems methodology is a learning, not an optimizing system.

Lane ( 1994) argues that developments in soft OR have much in common with current developments in systems dynamics modelling practice, and therefore a dialoge between them would be mutually rewarding.

Characteristics of the dominant OR paradigm and an alternative OR paradigm are presented by Rosenhead (1989) below in Table 1.

Table1. Characteristics of the dominant OR paradigm and a reveral of them to envision an alternative paradigm (Rosenhead 1989, after lane)

Characteristics of the dominant OR paradigm 1. Problem formulation in terms of a single objective and optimization. Multiple objectives, if recognized, are subjected to trade-off on a common scale. 2. Overwhelming data demands with consequent problems of distortion, data availability, and data credibility. 3. Secientization and depoliticization; assumed consensus. 4. People treated as passive objects. 5. Assumes a single decision maker with abstract objective from which concrete action can be deduced for implementation through a hierarchical chain of command. 6. Attempts to abolish future uncertainty and pre-take future decision.

Characteristics proposed for an alternative OR paradigm 1. Nonoptimizing; seeks alternative solutions that are acceptable on separate dimensions without trade-off. 2. Reduced data demands, achieved by greater integration of hard and soft data with social judgments. 3. Simplicity and transparency, aimed at clarifying the terms of conflict. 4. Conceptualizes people as active subjects. 5. Facilitates planning from the bottom up. 6. Accepts uncertainty and aims to keep options open for later resolution.

Lane (1994) summarized the characteristics of hard and soft systems thinking below Table 2.

Table 2. The hard and soft traditions of systems thinking (adapted from Checkland 1985 by lane)

Hard systems thinking of the 1950s and 1960s 1. Oriented to goal seeking. 2. Assumes the world contains systems that can be engineered. 3. Assumes system models are models of the world (ontology-based). 4. Speaks of "problems" and "solutions." Advantege: Allows the use of powerful techniques. Disadvantages: May need professional practitioners. May lose touch with aspects beyond the logic of the problem situation.

Soft systems thinking of the 1980s and 1990s? 1. Oriented to learning. 2. Assumes the world is problematic but can be explored using system models. 3. Assumes system models are intellectual constructs (epistemology-based). 4. Speaks of "issues" and "accommodations." Advantages: Available to both problem owners and professional practitioners. Keeps in touch with the human content of problem situations. Disadvantages: Does not produce final answers. Accepts that inquiry is never-ending.

SYSTEM DYNAMICS AND CITY

Below, some of the developments on the line of Forrester's system dynamics model is presented. The conception and development of system dynamics took place during the late 1950's at M.I.T. under Forrester, and although early work was in the management field, the subject became primarily known during the late 1960's for it's application at the macro level in urban and global modelling by Foresster and Meadows.

Jacobsen (1984) states that a number of features of system dynamics methodology make it suitable for testing social theory. First, it is possible to handle many variables simultaneously, and study their fluctuations over time. Secondly, we can take account of multiple feedback loops in the system under investigation and study their mutual influences, again, over time. Furthermore, we do not have to stick to linear hypothesis, and can readily model any nonlinear relationship posited by the theory. Jacobsen, presents a system dynamics model to anchor it in social theory, and states that they have found a guasi-experimental procedure for testing macrosociological theories.

Wolstenholme (1983), reviews the development in the subject of system dynamics. He states that the subject satisfies many of the requirements of a general methodology, as amently sought within the system field, as well as being a sophisticated dynamic modelling technique. He presents a subject summary, where a clear split is made between the system description/gualitative analysis mode of system dynamics and the quantitative analysis mode using continuous simulation techniques. Burdekin (1979) shows the flexibility of urban dynamics method in dealing with the lack of the model's spatial dimension by developing a model which simulates the development of housing and industry over a city divided into 16 zones.

Madden (1979) criticizes Forrester's model on several points. He states that these models do not produce counter-intuitive results at all, and ceraful analysis of the assumptions in these models, and the links between them, show that the results are easily predictable. According to Madden, the faults of the model are firstly on the assumptions of the model and the relationships between variables that they develop, and secondly the methods they use to link these relationships in a dynamic way. Sayer (1976) criticizes conventional regional science and urban modelling, mainly arquing that modellers are using the wrong paradigm.

Wilson (1978) stated that Forrester's urban dynamics model provides a major challenge for regional science:new work will be generated within a number of different paradigms as a result of new (and not necessarily accepted) emphases established within a particular paradigm. Alfeld (1995) presents his five applications of urban dynamics. He mentions that the past twenty-five years have not traced urban dynamics kindly.

In urban planning in 1960's architecture was dominating the profession rather than social science. The concern was with the physical environment, and it dealt with social processes in relation to the physical form. The process is called environmental determinism, i.e. the environment affected social process rather than the reverse.

Recently the concept of "total environment", integrating natural, physical and social aspects and "strategic environmental assessment" in under discussion and application which is developed by the impact of systems analytýc and dynamic techniques

The practice of using system dynamics as a methodological tool concerning urban problems in Turkey is very much limited. Few academic studies are existing (Erkut, 1986) is one of the PhD thesis using urban dynamics approach. Whereas concerning systems approach, systems concept is widely used in planning studios. Richmond (1993)'s view on thinking skills are relevant for the case of planning studios.

The urban dynamics model, and extensions of them, should be a basis of future influence on political decision. First, when modified to reflect a city's specific features, the model can be employed as a policy guide for urban planning. Second extensions of the models can focus on specific urban issues such as education, transportation, and social integration. Third, the models can provide a basis for a clearer understanding of urban processes and a better informed perception of how different aspects of a city affect one another.

REFERENCES

1. Alfeld L.E., "Urban Dynamics-The First Fifty Years, System Dynamics Review, Vol 11, No. 3 (Fall 1995)

2. Breheny BM. "Systems Analysis in Planning: A Critique of Critiques p.107, Batty M., B.Hutchinson (Ed), Systems Analysis in Urban Policy-Making and Planning,, Plenum Press, NY, 1983.

3. Batty M., "On Systems Theory In Urban Planning" :An Assessment", p.423, Batty M., B.Hutchinson (Ed), Systems Analysis in Urban Policy-Making and Planning, Plenum Press, NY.1983.

4. Burdekin R., "A Dynamic Spatial Urban Model: A Generalization of Forrester's Urban Dynamics Model", Urban Systems (1979), Vol 4., pp.93-120.

5. Jacobsen, C., "Sociology and System Dynamics", Dynamica, Vol 10, Part I, Summer 1984.

6. Janet M. Gould-Kreutzer, "Foreword: System Dynamics in Education", System Dynamics Review, Vol 9, No.2 (Summer 1993).

7. Kreutzer J.M.G., Foreword: System Dynamics in Education, System Dynamics Review, Vol 9, No 2 (Summer 1983)

8. Lane D.C., "With a Little Help From Our Friends: How System Dynamics and Soft OR Can Learn From Each Other, Systems Dynamics Review, Vol 10, no. 2-3 (Summer-Fall 1994).

9. Madden, M., "Recent Developments in Urban Dynamics", Town Planning Review, Vol 50, No 2, April 1979.

10. Richmond B., "Systems Thinking: Critical Thinking Skills for the 1990's and Beyend", System Dynamics Review Vol.9, No.2. (Summer 1993).

11. Sayer, R.A, "A Critique of Urban Modelling", Progress in Planning ,Vol.6, Part 3, Eds. Diamond, J.B. Loughlin, Pergamon Press, Oxford, 1976.

12. Wilson, A.G., Review of "A Critique of Urban Modelling" by R.A. Sayer, Environment and Planning A, 1978, Vol 10, p.1086.

13. Wolstenholme, E.F., "System Dynamics: A System Methodology or a System Modelling Technique", Dynamica, Vol 9, Part II, Winter 1983.

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