Environmental Modeling within GIS

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Once again we need to make the distinction between linking GIS with established environmental simulation models and being able to carry out some forms of environmental modeling within GIS using cartographic processing and/or map algebra-type functionality. This distinction, though still relevant, has become blurred in recent years due to changes in the power of programming languages that are part of GIS and the advent of tools within GIS to assist programming efforts. The criticisms of speed and the difficulty of creating truly dynamic models discussed above still apply, but the effort to build embedded environmental models of increasing sophistication is ongoing. Stocks and Wise (2000) believe that the extended programming or scripting functionality (e.g., MapBasic in MapInfo) now available in one form or another for most off-the-shelf GIS packages, provide “an a priori case” for these tools to be used in implementing embedded environmental models.

A vendor approach is the ModelBuilder first available in the Spatial Analyst 2.0 extension for ArcView and now in ArcGIS. This provides a wizard by which data and “processes” (raster data operations) can be chained together into complex models that automate all aspects of an analysis including input/output, data conversion (vector to raster), overlay, interpolation, and reclassification as well as map algebra-type operations. Figure 7.7 shows the ModelBuilder interface in which a very simple operation of obtaining a DEM and calculation of a slope map has been entered. Subsumed within this simple model of applying a function to data to derive a new data layer includes the specification of function parameters, applying class intervals, parameters for visualization of the derived data, and its storage on disk. A more complex model for calculating wildfire hazard (first discussed in Chapter 5, Equation (5.2) and Figure 5.12), using two input data layers to derive three data layers that are numerically scaled (reclassified) and combined into a hazard model using weighted overlay.

Data and Information Quality Issues

KLIK SEMBARANG 3 X CLOSE TAB BARU KLIK GET LINK Get Link A universal concern with all information systems must be the quality of the data contained within them, hence, the well-known adage of the com- puter age: garbage in, garbage out. Nevertheless, it should be recognized that “errors and uncertainty are facts of life in all information systems” (Openshaw, 1989). The process of describing aspects of reality as a file structure on storage media requires a high level of abstraction, as was illustrated in Chapter 2. Thus, any attempt to completely represent reality in GIS, while no doubt resulting in robust and flexible data sets, would also result in large, complex, and costly data sets that would require a higher order of technology to handle them. Historically, a detailed consideration of data quality issues in GIS lagged considerably behind the mainstream of GIS development and application. This is evident from the growth of the relevant literat