What is GIS?
There is little doubt that we live in the age of technology, where computers influence our lives in ways unimaginable just a few years ago. GIS (Geographic Information System) is a profound application of computer technology that literally changes the way we look at the world around us. Used by scientific investigators, resource managers, market strategists, planners, teachers, and many others, GIS applications are restricted only by our imaginations.
MAPS
GIS allows us to create multiple-layered maps of geographic areas that include endless
information/data, including: physical, cultural, demographic, environmental, agricultural,
and much more. Normally, GIS
applications begin with spatial data, which is
basically a defined geographic location that may be as large as the Earth
itself, or as small as the community, neighborhood, and surrounding countryside
we live in. This spatial
perspective may be as realistic as a familiar map or satellite photograph.
It may also be in the form of raster data,
which is basically a grid or more abstract model of reality, where cells are
given values allowing for elaborate mathematical calculations. These maps may begin
by simply showing us where something is located, but then go on to show us how
“things” have changed over time, what patterns may exist, as well as
predicting what changes may occur given certain influences.
DATA/THEMES
Once the
geographical area is defined, data is then applied. This data is available by loading and activating
themes,
which can be turned on and off at will. An application of this might begin
with a featureless map of the world. To this map, we could apply various
themes, including: countries, cities, rivers and lakes, soil profile,
topography, vegetation, and so on. As we turn "on" countries and
rivers for example, we see our featureless map gain the outlines of countries
and the location of rivers. When we turn countries and rivers
"off," they disappear. By selecting certain themes, by turning
them on and off, we actually create layers of information.
ATTRIBUTE
TABLES
Making maps and applying data/themes
is only the beginning of GIS. Once we activate a theme, we are given
access to attribute tables, which are basically
database files that provide
additional data about the theme we've selected. So for example, if we've
selected the countries theme, we would gain access to a table that would provide
access to an incredible amount of information about countries: population,
location, area, doubling time, infanticide rates, etc.
QUERIES
From the attribute tables, we can create queries by
asking the computer to select only those countries that meet certain
requirements of our choosing. For example, we may want to identify only
those countries whose population is greater than fifty million or cover an area
greater than 1 million hectares. In other words, we can create formulas to
select for specific information.
THERE'S MORE
This is just the beginning of what GIS is capable of--not even the tip of
the iceberg. While highly specific data is available at a price, a vast
amount of data is free and easily available to download from the Internet.
Many state and federal agencies provide useable data, including: the EPA,
the Census Bureau, USGS, and NOAA to name just a few. Whether you're a planner
or interested in research, a market strategist or teacher, GIS has invaluable
applications. The possibilities are virtually unlimited.
Attribute table from ArcView showing data associated with the specific theme "countries." |
This table from ArcExplorer showing a query for rivers with a length greater than 100 km and less than 300 km.
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This picture show a query for landuse of areas greater than 20,000 m2 but less that 25,000 m2. Notice specific themes turned on and off and which are layered on top and which below. |
