GIS: An Overview

From Amanda Briney, Geography at About.com Intern
http://geography.about.com/od/geographyintern/a/amandabio.htm

Apr 6 2008
An Overview of Geographic Information Systems
The acronym GIS refers to Geographic Information Systems - a tool that allows geographers and analys
ts to visualize data in several different ways in order to see patterns and relationships in a given
area or subject. These patterns generally appear on
maps but they can also be found on globes or in reports and charts.
The first truly operational GIS appeared in Ottawa, Ontario in 1962 and was developed by Roger Tomli
nson of Canada's Department of Forestry and Rural Development in an effort to use map overlays for a
nalysis of various areas in Canada. This early
version was called CGIS.

The more modern version of GIS used today emerged in the 1980s when ESRI (Environmental Systems Rese
arch Institute) and CARIS (Computer Aided Resource Information System) created a commercial version
of the software that incorporated the methods of
CGIS, but also included newer "second generation" techniques.

Since then it has undergone a number of technological updates, making it an efficient mapping and in
formational tool.

How GIS Works
GIS is important today because it is able to bring together information from multiple sources so tha
t various types of work can be done. In order to do this though, the data must be tied to a specific
location on the Earth's surface. Latitude and
longitude are usually used for this and the locations to be viewed are attached to their points on t
he geographic grid.
In order to then do an analysis, another set of data is layered on top of the first one to show spat
ial patterns and relationships. For example, elevation at specific locations can show up in the firs
t layer and then rates of precipitation at various
places in the same area can be in the second. Through a GIS analysis patterns about elevation and th
e amount of precipitation then arise.

Also important to the functionality of GIS is the use of rasters and vectors. A raster is any type o
f digital image, such as an aerial photograph. The data itself however is depicted as rows and colum
ns of cells with each cell having a single value.
This data is then transferred into GIS for use in making maps and other projects.

A common type of raster data in GIS is called the Digital Elevation Model (DEM) and is simply a digi
tal representation of topography or terrain.

A vector is the most common way data is shown in GIS however. In ESRI's version of GIS, called ArcGI
S, vectors are referred to as shapefiles and are made up of points, lines, and polygons. In GIS, a p
oint is the location of a feature on the geographic
grid, such as a fire hydrant. A line is used to show linear features like a road or river and a poly
gon is a two dimensional feature that shows an area on the earth's surface such as the property boun
daries around a university. Of the three, the points
show the least amount of information and the polygons the most.

The TIN or Triangulated Irregular Network is a common type of vector data that is capable of showing
elevation and other such values that change consistently. The values are then connected as lines, f
orming an irregular network of triangles to
represent the land's surface on a map.

In addition, GIS is capable of translating a raster to a vector in order to make analysis and data p
rocessing easier. It does this by creating lines along the raster cells that have the same classific
ation to create the vector system of points, lines,
and polygons which make up the features shown on the map.


The Three GIS Views
In GIS, there are three different ways in which data can be viewed. The first is the database view.
This consists of the "geodatabase" otherwise known as the data storage structure for ArcGIS. In it,
data is stored in tables, is easily accessed, and is
able to be managed and manipulated to fit the terms of whatever work is being completed.
The second view is the map view and is the most familiar to many people because it is essentially wh
at many see in terms of GIS products. GIS is in fact a set of maps that show features and their rela
tionships on the earth's surface and these
relationships show up most clearly in the map view.

The final GIS view is the model view which consists of tools that are able to draw new geographic in
formation from existing datasets. These functions then combine the data and create a model that can
provide answers for projects.


Uses of GIS Today
GIS has many applications in various fields today. Some of which include traditional geographically
related fields like urban planning and cartography, but also environmental impact assessment reports
and natural resource management.
In addition, GIS is now finding its place in business and related fields. Business GIS as it has com
e to be known is usually the most effective in advertising and marketing, sales, and the logistics o
f where to locate a business.

Whichever way it's used though, GIS has had a profound influence on geography and will continue to b
e used in the future as it allows people to efficiently answer questions and solve problems by looki
ng at easily understood and shared data in the form
of tables, charts, and most importantly, maps.