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Geographic Information System (GIS)
What is GIS?
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Examples of of GIS output that can be obtained from a single map. (Hold your mouse over each map for a description.)
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GIS (Geographic Information System) is a computer-based tool combining computer mapping and database technologies for the mapping and analysis of physical features and events. GIS has evolved over the past 30 years along with computer hardware and software technology, but its concepts have remained the same. GIS technology integrates powerful database functions such as querying and
statistical analysis with the visualization and geographic analysis benefits offered by digital maps drawn with a computer mapping system. GIS goes beyond conventional cartography by allowing the user to analyze data relating to specific locations on the earth.
In any computer mapping system, data in the electronic drawing is segregated on layers (think of stacked transparencies) according to some unifying feature. To use an architectural drawing as an example, a building’s walls will be on one layer, text on another, and plumbing fixtures on yet another. A drawing for a small residence can have dozens of layers, so that sets of drawings
produced for the electrician can be different from those given to the carpenter, yet all this information can coexist in a single computer file.
With GIS, such physical features as city streets, county roads, parcels, building outlines (known as “footprints”), water lines, and so on, will have their own layer, which not only vastly simplifies the process of drawing the maps, but it allows data to be attached to these layers that is significant to the feature represented on that layer. Each feature is then linked to it’s
position on the graphical image of a map, which in turn links it to a database which contains information about it. What was once a paper map limited by printing technology and the limits of human visual acuity, we now have computer drawn maps and databases, linked together to provide a wealth of information and to allow users an unprecedented degree of tracking of physical data and
events.
Printed maps are abstractions of the real world, a sampling of important elements portrayed on paper with symbols to represent physical objects or features. Topographic maps, for instance, use contour lines to show the shape of land surface. The actual shape of the land can only be supposed and visualized in the mind. Graphic display techniques in GIS make relationships among map
elements visible, heightening a person's ability to extract and analyze information. This information can then be used to generate statistics, measure distances and areas, develop new cartographic models, propose new sets of research questions, or design and print hard copy maps or maps viewable on the web. These abilities distinguish GIS from
other information systems and make it valuable to a wide range of public and private enterprises for explaining events, predicting outcomes, and planning strategies.
The Cartography and Geographic Information Society defines GIS as “automated systems used to capture, edit, store, manipulate, analyze and display a variety of spatial data". A GIS has three major components: a data base, a
spatial analysis and modeling capability, and a means for graphic display,” in other words, mapping software that relates geography to data. The maps created by GIS have many ways to represent geography. For example, a line can depict a road, a point can show the location of a building, and a polygon can represent a municipal boundary. Each of these features is linked to a database
that contains pertinent information. For example, if you selected a line that represents a road, the database would have information on who owns the road, the length of the road, the road’s classification, and the name of the road.
The information that is part of the map is displayed with different layers. The layers can be selectively turned on and off to display various features of the map, so the same map can be useful to a variety of people. The villages layer and the roads layer could be turned on so that transportation patterns could be discussed, then such layers as lakes, airports, and parks could be
added to the display, so that access to recreational activities could also be discussed. The user of the GIS software opens the database that is linked to the features displayed, and can turn layers on and off as needed. With a paper map, features cannot be selectively shown, and detailed information about the features can not be included on the map, but with GIS, any configuration of
layers can be displayed and the database information can be limitless. It is these qualities that allow GIS to be such a powerful tool for many fields of work.
Many professions use GIS regularly, for example, environmentalists, city planners, utility companies, and developers all use GIS successfully. Each profession can decide which data and layers would be best to represent the information they require on their maps. The environmentalist might want to know where hazardous waste sites are located in relation to communities, so they can
mobilize support for restricting the location such sites. A city planner and developer could work together to analyzing vehicular and pedestrian traffic and create an aesthetically pleasing city streetscape. A utility company will need to know where the electric poles are located so that it can maintain appropriate maintenance schedules and records. A transportation company would want
to analyses of the proximity of potential transit riders in relation to transit routes so that it could better map its bus lines and schedules.
What for a GIS system is easy would be extremely difficult and time consuming to accomplish by conventional methods. It is this power of GIS—linking physical locations to the information in a database—makes these and countless other complex analyses possible, and helps GIS users make better decisions. Because of its usefulness and success, GIS has become an indispensable
software tool during the past decade.
How does the SMTC use GIS?
At the SMTC we use GIS for virtually all of our studies. As a transportation planning agency, the creation and use of maps is an integral part of what we do. We use GIS to display maps at public meetings and to include in our studies, and to analyze data.
Beyond simple mapping tasks, GIS is utilized as an aid in the decision making process for transportation planning. As an example, for the Environmental Justice Analysis, several datasets were gathered at the Block Group level from the 2000 Census and linked to the SMTC's GIS. Utilizing various methodologies in GIS, staff were able to map and analyze concentrations of minority,
low-income and elderly populations. In the analysis process, UPWP and TIP projects were also mapped in GIS. This enabled staff to spatially examine the SMTC's planning projects and their proximity to the population concentrations. The maps that resulted were included in the final report, and the content of the report was based on the analysis yielded in GIS.
What GIS data is available at the SMTC?
At the SMTC we use ESRI software (ArcView and ArcInfo), and our data are in shapefile format and coverage format, while most of the relating databases are in Microsoft Access. The SMTC owns many of the files relating to Onondaga County and the Central New York area. Some files we have created, and others we have acquired through
other agencies. The GIS data that is created by SMTC is available for public use; for data that is derived from another agency (e.g. Onondaga County, NYSDOT, etc.), contact the appropriate agency.
GIS-related websites
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