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Geographic Information Systems

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Geographic Information Systems

Geographic Information Systems Geographic information systems (GIS) technology can be used for scientific investigations, resource management, and development planning. For example, a GIS might allow emergency planners to easily calculate emergency response times and effected areas of the ocean during an oil spill based on the spills location. You may ask, what is GIS? In the strictest sense, a GIS is a computer system capable of assembling, storing, manipulating, and displaying geographically referenced information, i.e. data identified according to their locations. Practitioners also regard the total GIS as including operating personnel and the data that go into the system. A geographic information system (GIS) works in a series of steps, First there is the relating information from different sources. If you could relate information about oil spill location to the oceans surface currents, you might be able to tell where to start clean up based on how long the oil has been in the ocean. A GIS, which can use information from many different sources, in many different forms can help with such analyses. The primary requirement for the source data is that the locations for the variables are known. Location may be annotated by x, y, and z coordinates of longitude, latitude, and elevation and any variable that can be located spatially can be fed into a GIS. Several computer databases that can be directly entered into a GIS are being produced by Federal agencies and private firms. Different kinds of data in map form can be entered into a GIS. A GIS can also convert existing digital information, which may not yet be in map form into forms it can recognize and use. For example, digital satellite images can be analyzed to produce a map like layer of digital information about marine life productivity. Likewise, sea-grass data can be converted to map-like form, serving as layers of thematic information in a GIS. Next Step for Geographic information systems (GIS) would be to Capture the data If the data to be used is not already in digital form, that is, in a form the computer can recognize, various techniques can capture the information. Maps can be digitized, or hand-traced with at computer mouse, to collect the coordinates of features. Electronic scanning devices will also convert map lines and points to digits. A GIS can be used to emphasize the spatial relationships among the objects being mapped. While a computer-aided mapping system may represent a shoreline simply as a line, a GIS may also recognize that shoreline as the border between ocean and land, and correctly display the tidal differences of the shoreline based on its location on the earth. Data capture, putting the information into the system, is the time-consuming component of GIS work. Identities of the objects on the map must be specified, as well as their spatial relationships. Editing of information that is automatically captured can also be difficult. Electronic scanners record blemishes on a map just as faithfully as they record the map features. For example, a fleck of dirt might connect two lines that should not be connected. Extraneous data must be edited, or removed from the digital data file. After the data is collected we must integrate the data. A GIS makes it possible to link, or integrate, information that is difficult to associate through any other means. Thus, a GIS can use combinations of mapped variables to build and analyze new variables. Before the digital data can be analyzed, they may have to undergo other manipulations - projection conversions, for example - that integrate them into a GIS. Projection is a fundamental component of mapmaking. A projection is a mathematical means of transferring information from the Earth's three-dimensional curved surface to a two-dimensional medium - paper or a computer screen. Different projections are used for different types of maps because each projection is particularly appropriate to certain uses. For example, a projection that accurately represents the shapes of the continents will distort their relative sizes. Since much of the information in a GIS comes from existing maps, GIS uses the processing power of the computer to transform digital information, gathered from sources with different projections to a common projection. Can a seabed map be related to a satellite image of marine life, as indicator of the importance of seabed to marine life productivity? Yes, but since digital data are collected and stored in various ways, the two data sources may not be entirely compatible. So a GIS must be able to convert data from one structure to another. Image data from a satellite that has been interpreted by a computer to produce a marine life productivity map can be "read into" the GIS in raster format. Raster data files consist of rows of uniform cells coded according to data values. Raster data files can be manipulated quickly by the computer, but they are often less detailed an

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