Integration of Raster-based GIS and system dynamics and its application

Integration of Raster-based GIS and system dynamics and its application

Pitan Singhasaneh, Dr. Apisit Eiumnoh, Dr. John E. Lukens, Dr. Harvey Demaine
Asian Institute of Technology
Bangkok, Thailand

Abstract
Some of the existing systems can be analyzed not only from its dynamical aspect or geographical aspect, but simultaneously from both. Integration of Geographic information system and system Dynamics provide us a more thoroughly understanding of the behavior of these systems. Apple computer and SuperCard software were chosen as tools for the development of this integrated program, using Collected data of pattaya city of Thailand, a model was developed for the simulation of a land use change.

Introduction
At the present, Geographical Information Systems (GIS) and system Dynamics can still be considered as a scientific tools in the developing stage. They are gaining popularity because of the usefulness in their own fields. At one end, GIS deals with the data, their position in coordinate system, their attributes, and their spatial interrelation with each other, while system Dynamics tries to understand problems which are dynamic (involve quatities which change over time) , and also, involve the notion of feedback.

GIS packages and system dynamics packages have their own strengths and weaknesses. They are summarized in the following table :

	GIS	System dynamics
GIS capability
-position with respect to a known coordinate system	Yes.	Yes, can be done using 'array' in Dynamo III, with severe limitation
-attributes of each point in the coordinate system	Yes.	Yes.
- spatial interrelations with each other Producting	Yes.	Yes.In a certain way.
-Producing 'Thematic' map	Yes	No.
Modelling capability
-repetitive calculation	No (Canbe done manually)	Yes.
-dynamic	No. (can be done manually)	Yes.
-feedback	No.	Yes.
-producing graphs of any variable over time	No	No

In other words, GIS is not made for analyzing systems whose value of factors over time (repetitive computation needed), and system Dynamics is not made for dealing with spatial relationship. This, of course, creates a gap between the two methods, which limits the study and in in-depth understanding of any systems falling inside this

Literature review
Up to now, there has been no reports or papers concerning the integration of system Dynamics and GIS. All of the paper found involved only one or the other Definitions.

System Dynamics
System dynamics is a methodology for understanding certain kinds of complex problems (Alexander and Pugh, 1981). It is originally introduced by Jay W. Forrester in the 1950's. The problems have at least two features in common; they are dynamic, and they involve the notion of feedback. Dynamic systems involve quantities that change over time. The thing which is responsible for this change is called feedback process.

Loop processes of feedback processes are formed chains of links connected together into a closed -path. They can be classified into two categories by the type of behavior generated by each.
1. Negative Feed back Loops
  These are loops that negate changes. They are also called "stabilizing" "equilibrating", "goal - seeking"' "self-correcting"' regulating", "homing -in" and others. This is because, they seek to maintain the status quo and resist changes.
2. Positive Feedback Loops
  They are loops that a accumulate change. They are called "destabilizing", "dis-equilibrating", "self-reinforcing", " runaway"., "growth", etc. They can be either "Vartuous", which are desirable , or " Vicious, which are not.
Geographical information System (GIS)
Geographical Information system is any whose data describes objects from the real world in terms of (1) their position with respect to a known coordinate system, (2) their attributes that are unrelated to position, and (3) their spatial interrelations with each other which describe how they are linked together or how one can travel between them (Burrough, 1986). It is also called a computerized mapping system for capture, storage, retrieval, and analysis of spatial and descriptive data.¹

GISs contain four Major Components²:
1. a data input subsystem that collects and processes spatial and descriptive data derived from maps, remote sensors, and other sources,
2. a data storage and retrieval subsystem, or database management systems,
3. a data manipulation and analysis subsystem that consists of evaluation functions, simulation models, and
4. a data -reporting subsystem for display of portions of the original database as well as manipulate data.

Objectives of the study
The immediate objective of this project is to demonstrate the importance of the integration of system Dynamics (SD) and Geographic Information System (GIS) . To do this, a "SuperCard" program will be written with the capacity of dynamically simulating a particular model through 'STELLA' and displaying outputs in GIS'S raster format.

The program is also hoped to be useful in; (1) gaining insights and understanding of a relationship between SD and GIS, (2) analyzing a real world problem, for example , model-based policy analyses, which involve the use of the model to help investigate why particular policies have the effects they do and to identify policies that can be implemented to improve the problematic behavior of the real system, and (3) assisting in better and improved decision making in land and other natural resource management in other areas, which furthermore, promotes economic growth and better living conditions of the people.

The developed program

Technical Data

Hardwares:	Macintosh IIci, 4 MB RAM, 80 MB HD
Softwares:	STEELLA for business, STEELLAStack, Super Card.
Data Structure:	Raster -based GIS

Design capability of the Program

The program will be designed to, have the following capabilities:
1. Store input data and display GIS maps on computer screen,
2. GIS's overlaying capability
3. Simulate System Dynamics models through STELLA, and display the output in the form of GIS map,
4. Real Number Handling Ability. Not like some GIS systems, it will be able to store information of each cell in a form of real numbers. This is very useful in some cases where it is essential to use real numbers in the calculation.
5. The program is also intended to be interactive, which means that, during the running of the program, the user will be able to change the value of variable (s) or put in/take out constraints from the model. This will be very useful in learning and understanding the dynamics of the model and the impact of each variable having on the model in greater details.
General Structure of the Program

* Arrows represented communication links.

Program written in SuperTalk
The general structure of the program is illustrated above. GIS part and system Dynamics part are linked by SuperCard's script. STELLA kernel is acting like a communication bridge between the program and the STELLA's model, carrying information to and during the simulation. The following section briefly explains how the program works.
1. The program gets necessary information from the user to prepare suitability map(s)
2. it gets initial value (s) from the user to run STEELA's model,
3. it runs the model by sending data through STELLA kernel,
4. it receives the feedback from the model through STEELS kernel,
5. it uses new information to display the output geographically,
6. the suitability map(s) is are updated,
7. if the predefined condition (s) is (are) not satisfied, then the updated information will be used and step (c) will be repeated again .
Communication between the program and STELLA

The communication link between super card and STELLA, is in the form of 'resource 'which has to be ' loaded' into SuperCard's program. This resource, called the STELLA kernel, is an XCMD (External command) written by high performance Systems, Inc. (the one who wrote STEELLA). It is portion of the STELLA source code which enable STELLA to simulate models built with the STELLA software.
Development of the Program

The program will be tested by running three different SD models on it . The first two models are simple models, used for the purpose of checking the program's bug and the overall performance, where the third model is used to demonstrate of the applicability of the program to the real world model.

This project has come to the final phase, dealing with the simulation of land use change of Pattaya city, The reasons why pattaya was chosen are; 1) Pattaya is relatively small city, comparing to Bangkok, which reduces the size of the area that has to be handled, and allow us to use higher map resolution, 2) it is one of the fastest growing city in Tailand, which shows a big change in land use pattern within a short period of time, and 3) it is easy collect data because of the short travel distance from Bangkok.

Pattaya's 1987 land use map, 1988 planned land use map, and road map have been digitized using ArcInfo package. The resolution of these map is chosen to be approximately 100 m 100 m., resulting in 91x1154 cell map. The greater resolution may be used in the future. The following diagram shows the process of preparing the data for the program.

At the moment, the Pattaya Model is sill under development. The original program has to be modified due to the change of map size. In the first two models, the maps were of smaller sizes, comparing with 91 by 154 cells pattaya map. The increase in the size of the data slows down the program speed considerably. This is because SuperCard is using a very-high-level-language (Super Talk) which uses interpreater, not compiler, to run the program.

One of the solution to the speed problem is to write a PASCAL resources and embedded them inside the main program. This process will increase the program's speed by assigning routines that are complex and need a lot of calculating power to the PASCAL resources while maintaining overall simple structure of SuperCard program.

Conclusions and recommendations
It is no doubt that the concept of integrating System Dynamics and GIS is possible. This proves to be another valuable step into a science of simulation and prediction of any dynamically GIS system. The speed of the program is only a temporary problem since the support of this aspect is little to none. More in depth study in SuperCard's XCMD and XFCN structure is needed to improve the performance of the program.

Words Worth Knowing

The following are the list of technical words which the author thinks the user may need to know. For more details, see SuperCard manual

External Commands , or XCMD's are externally written programs that were used extend what Hyper Talk could do. The programs were saved as resources and again added, it was treated as. if it were just another Hyper Talk command.
External functions, or XFCNs are also externally written programs that were used to extend HyperTalk . XFCNs, like normal HyperTalk functions, were used to return some sort of value instead of performing an action.
Resources are the traditional building blocks of all Macintosh programs. Everything from the dialog boxed and menus used in a traditional program to the code itself is stored in separate resources. Once solely the domain of the programmer, HyperCard brought such resources as sounds, XCMDs, XFCNs and icons into more common use.
Sounds are simply addition digitized sounds beyond the beep, boing, and harpsichord sounds that came included with HyperCard . New sounds could be recorded with a hardware digitizer like the MacRecorder from Farallon and saved as resources in HyperCard documents or HyperCard itself.
STELLA is an application for Macintosh computers, which can built the model and simulate it dynamically.
STELLA Stack is a HyperCard Stack which contains what's called " The STELLA Kernel". The STELLA Kernel is that portion of the STELLA code which enables STELLA to simulate models built with the STELLA software . The kernel does not contain any of the code which allows someone working with the STELLA software to build a model . Because STELLA Stack contains the STELLA kernel, it can simulate STELLA models. STELLA Stack therefore provides a way to simulate STELLA models from within HyperCard . Because STELLAStack communicates directly with STELLA models, it also can send data to, and bring data back from, these models.
Supercard is a unique application, It builds on the important accomplishment of Apple's program, HyperCard, to give you an environment in which you can build your own Macintosh programs using a wide variety of media - text, graphics, animations, and sound.
SuperTalk is the language used to create SuperCard scripts. You use scripts to manipulate Super Card objects and the data contained in those objects . SuperTalk's words and phrases perform actions, change object properties and monitor the SuperCard environment for events.

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1. Coulson, R.N., L.J. Folse, and D.K. Loh, "Artificial Intelligence and Natural Resource Management", Science, vol. 237, pp.262-267
2. D.E. Marble, H.W. Calkins, and D.J. Peuquet, Basic Readings in Geographic Information Systems ( SPAD Systems, Williamville, N.Y., 1984)