What is GIS?
A Geographic Information System, or GIS is an organized collection of computer hardware, software, and geographic data designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information. Or, in simple terms:
A computer system capable of holding and using data to describe places on the earth’s surface.
Many computer programs, such as spreadsheets, statistics packages or drafting packages can handle simple geographic or spatial data, but this does not necessarily make them a GIS. A true GIS links spatial data with geographic information about a particular feature on the map. For example, the centerline that represents a road on a map doesn’t tell you much about the road except its location. To find out the road’s width or pavement type, you must query the database. Using the information stored in the database, you could create a display symbolizing the roads according to the type of information that needs to be shown.
In short, a GIS doesn’t hold maps or pictures – it holds a database. The database concept is central to a GIS and is the main difference between a GIS and drafting or computer mapping systems, which can only produce a good graphic output. All contemporary geographic information systems incorporate a database management system.
A GIS provides the ability to associate information with a feature on a map and to create new relationships that can determine the suitability of various sites for development, evaluate environmental impact, identify the best location for a new facility, and so on.
Questions a GIS can answer
A GIS can be used to address many types of problems. For any application there are five generic questions that a sophisticated GIS can answer.
1. Location: What is at a given location?
GIS can be used to answer questions about what exists at a particular
location; questions such as where are the schools, where are the water lines,
or where are the hospitals. For each of these locations additional
information can often be gathered such as the name of the school; the size of
the water line and when it was last maintained; or the owner and name of the
hospital.
2. Condition: Where does something occur?
By using a method known as spatial analysis, a GIS can search for a
location where certain conditions are satisfied. For example, where are all
the parks with baseball fields or where are all of the residential properties
greater than 1 acre in size.
3. Trends: What has changed since…?
Determining trends involves a combination of location and condition and
seeks to find the differences within an area over time. Changes in crime
statistics within a specific area over time is one example of a trend that can
be analyzed using GIS.
4. Patterns: What spatial patterns exist?
The geographic distribution of data within an area and the presence of a
pattern can help identify or lead to possible solutions. Determining whether
cancer is a major cause of death among residents near a nuclear power
station is one example. Just as important is knowing how many anomalies
there are that don’t fit the pattern and where they are located.
5. Modeling: What if…?
“What if…” questions are posed to determine what happens when things
change. For example, what if a new building is added to downtown or a
neighborhood, how will it impact the surrounding area. Answering this type
of question requires geographic data as well as other information.
6. Routing: How can I get there?
GIS can help improve the delivery of services by determining the quickest or
shortest path between two places or by change previous directions due to
closed bridges or road construction.
A GIS is not…
…simply a computer system for making maps, although it can create maps at different scales, in different projections, and with different colors. A GIS is an analytical too. The major advantage of a GIS is that it allows the identification of spatial relationships between map features. A GIS does not store a map in any conventional sense; nor does it store a particular image or view of a geographic area. Instead, a GIS stores the data from which you can draw a desired view to suit a particular purpose.
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