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What is GIS?

Hardware - Software - Data - Vector Data - Raster Data - Thematic Data - Pictures - Metadata

This is probably the most asked question posed to those in the Geographic Information Systems (GIS) field and probably the hardest to answer in a succinct and easy manner.

GIS is an amazing combination of a computer application used to store, view, and analyze geographical information, especially maps.  From its early beginnings in the 1960’s, when it was discovered that maps could be programmed using simple code and then stored in a computer allowing for changes to be made when necessary.  This was a big step forward in the development of cartography when maps were painstakingly created by hand.  Even small changes sometimes required the creation of an entire new map.  The earliest version of GIS was known as computer cartography and used simple line-work to represent land features.  Later developments created the idea of overlaying different map features on top of each other to determine patterns and causes of spatial phenomenon.

The capabilities of GIS are a far cry from the simple beginnings of computer cartography.  At the simplest level, GIS can be thought of as a high-tech equivalent of a map.  Not only can paper maps be produced much quicker and more efficiently, the storage of data in an easily accessible digital format enables complex analysis and modeling not previously possible.  The reach of GIS expands into all fields and has been used for such widely ranged problems as prioritizing sensitive species habitats to determining optimal real estate locations for new businesses.

The key word to this technology is Geographic.  This usually means that the data (or at least some proportion of the data) is spatial.  Spatial is data that is referenced in some way to locations on the Earth.  Joined with this data is data usually known as attribute data. Attribute data is generally defined as additional information, which can then be tied to spatial data.  An example of this would be schools. The actual location of the schools is the spatial data.  Additional data such as the school name, level of education taught, school capacity, etc. would make up the attribute data.  It is the partnership of these two data sets that enables GIS to be such an effective problem solving tool.

GIS operates on many levels.  On the most basic level, GIS is used as computer cartography or mapping. The real power in GIS is through using spatial and statistical methods to analyze attribute and geographic information.  The end result of the analysis can be derivative information, interpolated information or prioritized information.


Hardware comprises the equipment needed to support the many activities of GIS ranging from data collection to data analysis.  The central piece of equipment is the workstation, which runs the GIS software and is the attachment point for auxiliary equipment.  Data collection efforts can also require the use of a digitizer for conversion of hard copy data to digital data and a GPS data logger to collect data in the field.  The use of handheld field technology is also becoming an important data collection tool in GIS.  With the advent of web-enabled GIS, web servers have also become an important piece of equipment for GIS.


Different software packages are important for GIS.  Central to this is the GIS application package. Such software is essential for creating, editing and analyzing spatial and attribute data, therefore these packages contain a myriad of GIS functions inherent to them. Extensions or add-ons are software that extends the capabilities of the GIS software package. For example, XTools is an ArcView extension that adds more editing capabilities to ArcView 3.x. Component GIS software is the opposite of application software.  Component GIS seeks to build software applications that meet a specific purpose and thus are limited in their spatial analysis capabilities. Utilities are stand-alone programs that perform a specific function. For example, a file format utility that converts from one type of GIS file to another. There is also web-GIS software that helps serve data through Internet browsers.


Data is the core of any GIS.  There are two primary types of data that are used in GIS.  A geodatabase is a database that is in some way referenced to locations on the earth.  Geodatabases are grouped into two different types:  vector and raster.  Coupled with this data is usually data known as attribute data. Attribute data generally defined as additional information, which can then be tied to spatial data. Documentation of GIS datasets is known as metadata.


Vector data is split into three types:  polygon, line (or arc) and point data.  
Polygon data is used to represent areas.  Polygon features are most commonly distinguished using a thematic mapping symbology (color schemes), patterns or numeric gradation.

Line (or arc) data is used to represent linear features.  Common examples would be road centerlines and hydrology.  Symbology most commonly used to distinguish arc features from one another are line types (solid lines versus dashed lines) and combinations using colors and line thicknesses.

Point data is most commonly used to represent nonadjacent features.  Examples would be schools, points of interest, hospitals, fire stations, libraries, etc.  Point features are also used to represent abstract points. For instance, point locations could represent city locations or place names.

Both line and point feature data represent polygon data at a much smaller scale.  They help reduce clutter by simplifying data locations.  As the features are zoomed in, the point location of a school is more realistically represented by a series of building footprints showing the physical location of the campus.  Line features of a street centerline file only represent the physical location of the street. If a higher degree of spatial resolution is needed, a street curb width file would be used to show the width of the road as well as any features such as medians and right-of-ways (or sidewalks).


Raster data are cell-based spatial datasets. There are also three types of raster datasets:  thematic data, spectral data, and pictures.


Spectral data presents aerial or satellite imagery which is then often used to derive vegetation or geologic information by classifying the spectral signatures of each type of feature.


What results from the effect of converting spatial data location information into a cell based raster format is called stairstepping.  The name derives from the image of exactly that, the square cells along the borders of different value types look like a staircase viewed from the side.

Unlike vector data, raster data is formed by each cell receiving the value of the feature that dominates the cell.  The stairstepping look comes from the transition of the cells from one value to another.


Metadata, as best described by a GIS professor is, “Data about Data.”  The metadata describes in further detail, what the data includes, where it came from and how it is used.  A good example would be a portable music player, like an iPod.  The album names, song titles, and album art embedded in the music files are used to generate the artist and song listings, would be the metadata.