ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - GEOGRAPHIC INFORMATION SYSTEMS doc

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ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - GEOGRAPHIC INFORMATION SYSTEMS doc

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425 G G EOGRAPHIC INFORMATION SYSTEMS The term “Geographic Information System” (GIS) varies as a matter of perspective, and ranges in scope from specific computer software packages to software, hardware and data, to software, hardware, data, and support personnel. The most exhaustive definition is given by Dueker and Kjern as: Geographic Information System—A system of hardware, software, data, people, organizations, and institutional arrangements for collecting, storing, analyzing, and dissemi- nating information about areas of the earth. While this is an all-inclusive definition, the software packages at the heart of a GIS have their roots in the work of two researchers at Ohio State University, Marble and Tomlinson, in the mid to late 1960s. These men coined the phrase “Geographic Information System,” and defined a GIS as having the following four components: 1. Data Input and the ability to process data. 2. Data Storage and Retrieval with the ability to edit. 3. Data Manipulation and Analysis. 4. Data Reporting Systems for the display of tabular and graphic information. Data input, storage/retrieval, and reporting were (and still are) common to two other computer software packages— Computer Assisted Mapping (CAM) and Database Management Systems (DBMS) which separately managed graphical and tabular information. The development of GIS combined these packages to provide what many refer to as “intelligent maps,” which are maps with extended informa- tion. Extended information can include information from areas such as census, tax assessment, natural resources availability/quality, which may be linked to a map, but are managed as part of a separate database. However, the true distinction of a GIS is Marble and Tomlinson’s third component—the ability to analyze spatial information. The analysis capability enables a GIS to automatically evaluate information from several sources as a function of their spa- tial context. CAM systems may provide some of the same information as a GIS through a series of separate maps, but they require manual interpretation. There are six basic analytical questions which many GIS software packages are able to address, partially or in full. These are: 1. Location—“What is it?”—What types of features exist at a certain place, such as “What is the popu- lation of a given census tract?” 2. Condition—“Where is it?”—Finding a site with certain characteristics, such as “Which agricul- tural fields are within 100 meters of a stream?” 3. Trend—“What has changed?”—Evaluation of spatial data as a function of time. 4. Routing—“Which is the best way?”—A variety of problems to determine paths through a network, such as finding the shortest path or optimum flow rates. 5. Pattern—“What is the pattern?”—A function which allows environmental and social planners to account for spatial distribution. Examples include the spread of diseases, population distribution versus urban development, or targeting specific consumer trends. 6. Modeling—“What if?”—Allow model develop- ment and evaluation, including “Monte Carlo” evaluation, where a variety of factors influence a situation, and their relationship is determined by varying one factor while holding the others constant. A GIS is able to perform the above operations because they maintain the topology, or spatial associations, of the elements of their database. For example, an individual look- ing for 617 East Central Avenue on a map is able to see that this address is between 6th and 7th streets, on the south side of the street. Furthermore, if the individual wants to drive © 2006 by Taylor & Francis Group, LLC 426 GEOGRAPHIC INFORMATION SYSTEMS to this address and the map indicates that these streets are one-way in given directions, they are able to plan their route accordingly. A GIS may perform the same operation because it has the same information—that 6th and 7th intersect Central Avenue, the directed flow of traffic on these streets, and the distinction of areas on the left and right side of a line. This case is an example of what is called a “vector format” GIS, where space is represented by a two dimensional mani- fold of polygons (city blocks) which are bounded by a set of directed line segments (streets). The other format by which a GIS may represent spa- tial data is referred to as “raster format.” In this format, an area or volume is represented by a two or three dimensional matrix of uniform data elements, called “grid cells.” Grid cells are the smallest areas that this type of GIS may resolve and are artificial constructs uniform in size and shape and are considered to have homogeneous data properties. An example would be a Soil map represented as a series of 30 meter by 30 meter plots of ground, where each plot is con- sidered to be one particular type of soil, or a uniform blend of multiple soil types. An advantage of the raster format is the ability to show gradual changes and trends over a spatial area, because the matrix indices of the grid cell coordinates inherently imply the topology of the GIS data set. One of the disadvantages of the raster format is that data in the “real world” may not conveniently break down into uniform grid cells. Consequently, using this format involves an optimiza- tion problem to select a grid cell resolution that adequately represent the given data set, while minimizing the database size. Decreasing the size of gird cells in a raster exponen- tially increases the database size. With the growing usage of Geographic Information Systems, there is a corresponding need for standardization. Standardization does not mean that all GIS databases con- tain the same format and quality of information; instead it provides a common terminology and format for maintaining appropriate metadata, or data about data. Currently in the United States, the official federal standard regarding GIS is the Spatial Data Transfer Standard, which provides a spe- cific terminology for GIS through a set of definitions and format for maintaining an appropriate spatial data quality report for metadata. The importance of providing a stan- dard, such as the SDTS, is that it provides the end user with and ability to assess whether or not the output from a GIS has the quality necessary to carry out further operations or analysis. Dueker and Kjern’s definition of a GIS is the most appropri- ate to consider, because the successful adoption of a GIS does not rely only on purchasing a software package. A GIS relies on people gathering the appropriate data, which is then input and manipulated in the GIS software environment, and which has knowledgeable individuals interpreting and analyzing results for their acceptability. Therefore, these elements must be considered as part of a Geographic Information System. REFERENCES Cooke, D.F., 1992, Spatial Decision Support System: Not Just Another GIS, Geo Info Systems, May 1992, pp. 46–49. Cowen, D.J., 1988, GIS versus CAD versus DBMS: What Are the Differ- ences Photogrammetric Engineering and Remote Sensing, Vol. 54, No. 11, pp. 1551–1555. Dueker, K.J., 1987, Geographic Information Systems and Computer Aided Mapping, APA Journal, Vol. 53, No. 3, pp. 383–390. Joffe, B.A. and B.S. Bergstrand, 1992, Managing Engineering Drawings in a GIS Environment, Geo Info Systems, April 1992, pp. 58–63. Huxhold, W.E., 1991, Information in the Organization, An Introduction to Urban Geographic Information Systems, Oxford University Press, New York, pp. 3–24. National Institute of Standards and Technology (NIST), 1992, Federal Information Processing Standard Publication 173: Spatial Data Trans- fer Standard, Part 1, U.S. Department of Commerce. TODD HEPWORTH University of Wisconsin © 2006 by Taylor & Francis Group, LLC . usage of Geographic Information Systems, there is a corresponding need for standardization. Standardization does not mean that all GIS databases con- tain the same format and quality of information; . EOGRAPHIC INFORMATION SYSTEMS The term Geographic Information System” (GIS) varies as a matter of perspective, and ranges in scope from specific computer software packages to software, hardware and. to Urban Geographic Information Systems, Oxford University Press, New York, pp. 3–24. National Institute of Standards and Technology (NIST), 1992, Federal Information Processing Standard Publication

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  • TABLE OF CONTENTS

  • PART: G

  • CHAPTER 30: GEOGRAPHIC INFORMATION SYSTEMS

    • REFERENCES

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