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GEOGRAPHIC INFORMATION SYSTEMS Exercise 2: Geographic Information Systems (GIS) REQUIRED MATERIALS 1. This lab manual. 2. Elemental Geosystems , 5 th edition, 2004, by R. Christopherson. 3. GIS database for Calvert County, MD--provided in computer laboratory. 4. Workstation running ArcGIS software--provided in computer laboratory. REQUIRED READING 1. This exercise—be familiar with all terms in bold . 2. Pages 25-32 in Elemental Geosystems . INTRODUCTION In the ArcGIS software, different data layers are called themes . The themes in the Calvert County database include county boundary, roads, water, major soils, elevation and land use. The object of the exercise will be to comprehend the basics of a GIS including the concepts of georeferencing, overlaying of the various themes, and spatial analysis of theme attributes. Each of the themes has an associated spreadsheet table that contains columns of information such as ownership, location, and size (area). Geographic Information Systems “Geographical information systems should be thought of as being very much more than a means of coding, storing, and retrieving data about aspects of the earth's surface. In a very real sense the data in a geographical information system ... should be thought of as representing a model of the real world. Because these data can be accessed, transformed, and manipulated interactively in a geographical information system, they can serve as a test bed for studying environmental processes or for analyzing the results of trends, or of anticipating the possible results of planning decisions. By using the GIS in a similar way that a trainee pilot uses a flight simulator, it is, in principle, possible for planners and decision-makers to explore a range of possible scenarios and to obtain an idea of the consequences of a course of action before the mistakes have been irrevocably made in the landscape itself.” -- From Burrough, P.A. (1986). Principles of Geographical Information Systems . Oxford: Clarendon Press, page 6. A Geographic Information System ( GIS ) is a “computer-based, data-processing tool for gathering, manipulating and analyzing geographic information” ( Geosystems , p.31). Geographic information systems are capable of assembling, storing, manipulating and displaying data according to their locations. They differ from digital cartography, spreadsheets, or other database management systems in that all data in a GIS is likely to be connected to real world coordinates. 13
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GEOGRAPHIC INFORMATION SYSTEMS Attribute information can be connected to features at a set of coordinates in a process called geocoding . Attributes (such as data in a spreadsheet) can be analyzed in a spatial manner by complex calculations (performed by the computer) and displayed in a map form. For example, using a GIS database with streetlights in a neighborhood represented by points with precise coordinates and a related table of attribute information which explains each light's details, a query of the database could ask for all streetlights with 60 watt bulbs, and a map could be drawn showing their location. Since most non-geographic information systems do not have the ability to
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