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GIS As A Supporting Tool In The Establishment of Land Use Road Density ModelMohamad Nor Said Department of Geoinformatics Faculty of Geoinformation Science & Engineering Universiti Teknologi Malaysia 81310, UTM Skudai, Johor, Malaysia Tel: +607-5530720, Fax: +607-5566163 m.nor@fksg.utm.my Muhammad Zaly Shah Department of Urban and Regional Planning, Faculty of Built Environment Universiti Teknologi Malaysia 81310, UTM Skudai, Johor, Malaysia Tel: +607-5530720, Fax: +607-5566163 b-zaly@utm.my ABSTRACT As a measure of accessibility, road density is an important indicator of urbanization. Areas that are highly accessible are those with high percentage of road density. However, providing respectable level of road density requires considerable planning as well as large amount of financial resources. Therefore, it is critical that only adequate road density required to guarantee continued growth is provided, nothing more. Realizing this fact, the Highway Planning Unit of the Malaysian Ministry of Works has awarded a contract research to the Universiti Teknologi Malaysia to study the relationship between the transportation (road density) and land uses with an expectation that a generalized empirical model can easily be used as a guide in road planning. In accomplishing the modeling tasks, Geographical Information System (GIS) has been identified as a tool in preparing land use datasets required to test and run the model in the process of determining the significant parameters that contribute to road density. Furthermore, GIS is also used as a graphical display tool in demonstrating the variation of existing and forecasted road density of the study sites. 1.0 Introduction One of the most productive and powerful innovations in Geographical Information System (GIS) has been the incorporation of modeling. This involves joining the GIS database to a computer-driven model of some process or procedure. The GIS can then combine pieces of data for every object, put it through the model process, and get back a new piece of information. This allows spatial data to be processed in mass quantities using powerful, complex formulas. There are two applicable types of modeling namely simulation and predictive models. Simulation modeling involves using the GIS to simulate a complex phenomenon in nature which generally requires a high degree of technical expertise and can vary in the degree to which it is linked to the GIS. However, once the GIS and the model are linked, they can be used to evaluate different features of the data, whether it is spatial or non-spatial. The predictive modeling, on the other hand, is a more powerful modeling tool where an expert acquires data and uses it to build a statistical model and then tested by regression analysis. Once the model has been tested on known data, it is applied to new data in order to predict results. This type of modeling has been used to predict processes like flooding, groundwater contamination, and soil loss. Similarly it is used to carry out the land use transportation (road density) interaction study which is the subject of this paper. The ability to link GIS to these models has greatly increased the usefulness of GIS as a scientific tool. With respect to the land use transportation (road density) interaction modeling, which is the subject of this paper, the predictive modeling is applied. The proposed model uses an open-source urban simulation application called UrbanSim where as many as eighteen independent variables involving two major towns (Johore Bahru and Kuantan,) are tested to determine the most significant parameters that contribute to the urban road density. In assisting the modeling process, a GIS (ArcView) is used to establish the geospatial database which includes data of various forms and from various sources. The model is regressed by least square fitting method and calibrated to study the level of acceptability. With the future land use plan the model is then used to predict the road density level and again GIS is applied to import the forecasted data and graphically display the distribution. The results demonstrate that only five variables show the significant effects on the road density with each town has its own combination of these parameters. 2.0 Simulating Land Use-Transportation Interaction 2.1 Functional Relationship Between Land Use And Transportation The demand for transportation is well understood to be derived from the demand in urban activity. Urban activity, on the other hand, is a function of land-use. Interestingly, the provision of transportation system (i.e. services and infrastructure) may also influence the development of land use. Thus, there is a clear interaction or cause-and-effect relationship between transportation and land-use (see Figure 1).  Figure 1: The inter-relationship between demand of transportation and development of land-use A land use-transportation interaction model, then, is a simulation model that combines theories, data and algorithms to represent the functioning of the land use and transportation systems. Once calibrated against a known scenario, this simulation model can be used to make predictions about the future. In urban and transportation planning, this ability of knowing the likely future is important as urban and transportation policies affect peoples lives. But, more importantly, the interaction model helps create sustainable cities as land use and transportation developments have their share of adverse impacts, e.g. social ills and environmental pollution. Existing transportation economic theories consider transportation as a derived demand of land uses (Blunden and Black, 1984). What this really means is that transportation in itself cannot exist except for providing accessibility to land uses or as a medium to move goods and services between land uses. Rarely do people travel for the sake of travelling. More often than not, people travel to obtain some perceived benefit at the destination, which is offered by the different land uses. Hence, the modeling of the interaction between land use and road transportation starts with a premise that future road transportation requirements are based on what land use changes that will be taking place (Miller, 2003). This relationship between land use and transportation activities is described graphically in Figure 2.  Figure 2: Relationship between land use and transportation activities (Source: Rosenbaum and Koenig, 1997) Mathematically, however, this relationship between road transportation and land uses can be expressed by the following functional relationship:  where:  = Estimated road transportation requirements (e.g. road density) at time t + 1 = Estimated land uses at time t + 1
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