What is GIS?

A Geographic Information System, or GIS, is an organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information. In simple terms:

A computer system capable of holding and using data describing places or events 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, GIS doesn't hold maps or pictures - it holds a database. The database concept is central to GIS and is the main difference between 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 gives you 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, determine why an event is occurring in this location, and so on.

GIS components

A GIS is a very powerful tool that can be used to capture, store and analyze geographic data but it is not, by any means, a stand-alone system. You need several other very important components to make up a GIS:

1. People

Without well trained, competent personnel operating and supporting a GIS the system would not function. Skill in selecting and using tools from the GIS toolbox, along with an intimate knowledge of the data being used, are essential to your success as GIS user. Just pressing a button is not enough.

Local GIS Contacts

2. Hardware

The enterprise GIS infrastructure within Dane County consists of numerous servers, workstations, PCs, printers and plotters. GIS software makes particularly high demands on computer hardware speed and resolution.  While some GIS functionality can be delivered using browser-based technology, detailed GIS analysis requires a high end workstation.

3. Software

In order to use GIS in the most efficient manner it is important to run an up-to-date version of the software.  Dane County uses a combination of ESRI and other commercially available GIS applications.  In addition, some customized GIS scripts and extensions have been developed for staff use. 

Dane County GIS Applications

4. Data

The heart of any GIS is the database through which questions such as what a feature is, where it is, and how it relates to other features can be answered. The Dane County digital map library is designed to allow any user on the GIS network to view county wide geographic data from a common source. The map library also provides an efficient and secure means of maintaining the database.  All Dane County enterprise GIS datasets have been documented with FGDC-compliant metadata and posted to the Wisconsin node of the National Spatial Data Infrastructure.

Questions a GIS can answer

Perhaps the simplest way to define a GIS is by listing the types of questions it can answer. For any application there are five generic questions that a sophisticated GIS can answer.

1. Location: What is at a given location?

The first of these questions seeks to find out what exists at a particular location. A location can be described as a place name, zip code or address.

2. Condition: Where does something occur?

Using spatial analysis the second question seeks to find a location where certain conditions are satisfied (e.g., an unforested section of land at least 2,000 square meters in size, within 100 meters of a road, and with soils suitable for supporting buildings).

3. Trends: What has changed since ...?

The third question might involve a combination of the first two and seeks to find the differences within an area over time.

4. Patterns: What spatial patterns exist?

You might ask this question to determine whether cancer is a major cause of death among residents near a nuclear power station. Just as important, you might want to know 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, for example, if a new road is added to a network. Answering this type of question requires geographic as well as other information.

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 tool. The major advantage of a GIS is that it allows you to identify the spatial relationship 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.

Source:  Volusia County, Florida and Dane County, Wisconsin