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Lakota Studies 400/600:  Special Topics:  Introduction to Geographic Information Systems and Science

Week 5 Notes:  Data Input and Output

Data Input and Output

Thus far, as we have progressed through the course, we have used data that is already collected--countries, counties, earthquakes, cities, and so on.  You have been learning various ways to ask questions of the data to make a decision about the Earth and its people.   But, can you enter your OWN spatial information into a GIS? Yes.  Entering spatial information into a GIS is one of the "core functions" of any GIS.  Collecting data is one of the most expensive parts of any GIS project, sometimes taking up to 85% of the total time for a GIS-based project.  Once the data has been gathered, it can be analyzed.  Sometimes, however, obtaining the data is the most difficult part of the project.

Input  

There are several ways of entering data into a GIS.  Remember that GIS data includes the spatial information and the attributes.  Entering the attributes is usually done by keying in documents by hand, with Optical Character Recognition, voice recognition, or by importing it from an existing spreadsheet or relational database.  

Entering spatial data is more complicated than the attributes.  One way to enter spatial information is to digitize, or manually enter the spatial coordinates by way of a mouse connected to a digitizing table or tablet.  An operator traces the outline of polygons, such as land holdings, or along lines such as streams, or clicks the mouse on a point such as a water well.  The table or tablet contains a fine grid of wires that capture the coordinates of where the mouse is located.  GIS labs used to be filled with digitizing tablets.  Why aren't the tablets as common today?  First, over the decades since the 1970s, spatial data has been collected by organizations around the world, lessening the data input burden for today's GIS users.  Second, other means may be more efficient than digitizing to collect spatial information, as will be discussed below.  Third, the digitizing that is done today is often done right on the screen, using a mouse, in a process known as "heads-up digitizing."  Most often, the data collector views a base map or image such an aerial photograph on the screen in a GIS, and traces features with a mouse on the screen.  The features are saved in a new point, polygon, or line layer.

Other means to enter data into a GIS besides digitizing include scanning.  Maps are scanned by drum (roll) scanners or large format flatbed scanners.  Once the data are scanned, they are in raster mode.  If vectors are desired (for example, if the map contains streams), the data must be vectorized and tagged in an automated or manual process.   Another means of input is via traditional surveying techniques, or with coordinates collected by Global Positioning Systems (GPS) receivers.  Descriptions of land ownership, or parcels, can be entered in a process known as COGO, or coordinate geometry.  Often, data such as imagery has been captured by a sensor on board an airplane or satellite, and that data can be brought directly into a GIS for analysis.  Data that has already been collected can be downloaded from the Internet, such as from www.geographynetwork.com, or obtained on a variety of media, such as CD-ROMs.   You will have the opportunity very soon to download data from the Internet for your GIS. 

Data Output 

There are several ways of outputting data FROM your GIS.  Displaying your data on the screen is the most common way of outputting data from a GIS, using maps symbolized as graduated colors, graduated symbols, charts, and so on.  You have already had the opportunity this semester to output data in some of these ways.  Printing is probably the second most common way of outputting your data.  You have already created several layouts in ArcView, and will have the opportunity to create more.  More and more, GIS users are outputting their data over the Internet, via Internet Map Server technology.  Users of the technology can query and access just the data that meets their needs in an interactive mode using a standard web browser.  We will be able to examine some of the sites that offer this service.

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Author:  Joseph J. Kerski, Geographer, USGS, jjkerski@usgs.gov, 303-202-4315