Related Pages:

• Selected Regional Submodels (Graph)
• Time & Space in Regional Models [Table]
• Spatial Interaction Perspectives [Table]
• "endogenous" and "exogenous" model components

Definition of a "Model":

1. A simple version: A model is a simplified representation of some aspect of the real world. (p.8)
2. A more complex version: A mathematical, logical or mechanical representation of a relationship, theory, process, system, or sequence of events, so designed that a study of the model functions as a means of summarizing the complex relations of the real world or as a way of illustrating a theory.

Purposes and Advantages (incl. pedagogic advantages) of Modeling:

• Models provide an economical description of the essential features of a complex situation
• The discipline of constructing models helps us to get our thinking straight; it makes us get down to fundamental principles; the process of modeling helps us to learn how to formulate problems better, (especially those broad, fuzzy problems where it is hard to know how and where to begin) and how to identify essential elements needed for moving toward explanation and for communicating with others.
• Formal analytical models enable us to use more variables than we can comfortably carry in our heads. By temporarily setting aside unimportant variables, they serve as powerful tools for the study of interrelationships among the important variables.
• As we use models more and more, we begin to develop analytic insights in other situations where we do not consciously engage in a modeling process.

Types of Models:
Flow Charts: A descriptive, diagrammatic model presenting situations where commodities (including information) or portions of populations pass through a system from one condition to another. Drawing boxes and showing the connections between them is a good way to attack problems associated, e.g., with student projects. If you find it difficult to draw up such a model, you probably do not understand all aspects of the system you are trying to model.

Decision Trees: Part of decision (including location decision) analysis. They help describe, organize, trace repercussions of and discriminate between alternative decisions.

Long Divisions (averages, percentages, coefficients, quotients; incl. the famous "Location Quotient"): Reduce the complexity and assist in comparisons of quantitative information.

Compound Growth Models: a simple, but formal mathematical model of cumulative change which describes explicitly the quantitative changes in a particular variable or system in response to specific stimuli. (Compound interest, net population growth models etc.)

Vicious Circles (Cycles): Cumulative models of change based on 'positive' feedback.

Descriptive Models: describe the way the world (actually but in simplified form) operates; show what outcomes may result from what action.

Prescriptive Models: go beyond descriptive models in that they also include procedures for choosing between alternative actions, given the decision-makers preferences among the outcomes.

Predictive Models rearrange the structure of a descriptive model so that variables of interest at the end of a causal sequence can be predicted from variables earlier in the sequence.

Theoretical or Conceptual Models have a high degree of abstraction, whiles empirical or operational models have a low level of abstraction and a basis in empirical and/or practical considerations.

Planning Models: allow alternative courses of action to be evaluated

Deterministic Models: Given the relationships, the initial conditions and the actions, the outcome is certain and uniquely determined.

Probabilistic (or Stochastic) Models: are based on relationships which are recognized as leading to variable outcomes which however can be probabilisticly predicted.

[Sources Edith Stokey & Richard Zeckhauser. A Primer for Policy Analysis, Ch.2; Goodall]

Other Literature:

• Anas, Alex. Modeling in Urban and Regional Economics. Harwood Academic Publishers, 1987.

• Ebert, Ronald and T.R. Mitchell, Organizational Decision Processes, 1975, Ch.7 "The Role of Models" pp.133ff.

• Lowry, Ira S., "A Short Course in Model Design," Journ. of the American Institute of Planners 31(1965), 158-65. Reprinted in Berry & Marble, eds., Spatial Analysis, 1968, pp.53ff.

• Plummer, Paul S., The Modeling Traditions, in: Sheppard, Eric and Trevor J. Barnes, eds., A companion to economic geography. Oxford, UK ; Malden, Mass. : Blackwell Publishers, 2000 [Suzzallo/Allen Stacks HF1025 .C66 2000]