|
|
|
|
Do
More With
Less
 |
|
|
|
|
|
|
|
|
Article > Geographic Information Systems (GIS)
 |
|
Introduction and Brief History
The advent of cheap and powerful computers over the last
few decades has allowed for the development of innovative
software applications for the storage, analysis, and display
of geographic data. Many of these applications belong to
a group of software known as Geographic Information Systems
(GIS). Many definitions have been proposed for what constitutes
a GIS. Each of these definitions conforms to the particular
task that is being performed. Instead of repeating each
of these definitions, I would like to broadly define GIS
according to what it does. Thus, the activities normally
carried out on a GIS include:
 |
The
measurement of natural and human-made phenomena
and processes from a spatial perspective. These
measurements emphasize three types of properties
commonly associated with these types of systems:
elements, attributes, and relationships. |
|
|
The
storage of measurements in digital form in a computer
database. These measurements are often linked to
features on a digital map. The features can be of
three types: points, lines, or areas (polygons). |
|
|
The
analysis of collected measurements to produce more
data and to discover new relationships by numerically
manipulating and modeling different pieces of data. |
|
|
The depiction of the measured or analyzed data in
some type of display - maps, graphs, lists, or summary
statistics. |
The first computerized GIS began its life in 1964 as a project
of the Rehabilitation and Development Agency Program within
the government of Canada. The Canada Geographic Information
System (CGIS) was designed to analyze Canada's national
land inventory data to aid in the development of land for
agriculture. The CGIS project was completed in 1971 and
the software is still in use today. The CGIS project also
involved a number of key innovations that have found their
way into the feature set of many subsequent software developments.
From the mid-1960s to 1970s, developments in GIS were mainly
occurring at government agencies and universities. In 1964,
Howard Fisher established the Harvard Lab for Computer Graphics
where many of the industries early leaders studied. The
Harvard Lab produced a number of mainframe GIS applications
including: SYMAP (Synagraphic Mapping System), CALFORM,
SYMVU, GRID, POLYVRT, and ODYSSEY. ODYSSEY was the first
modern vector GIS and many of its features would form the
basis for future commercial applications. Automatic Mapping
System was developed by the United States Central Intelligence
Agency (CIA) in the late 1960s. This project then spawned
the CIA's World Data Bank, a collection of coastlines, rivers,
and political boundaries, and the CAM software package that
created maps at different scales from this data. This development
was one of the first systematic map databases. In 1969,
Jack Dangermond, who studied at the Harvard Lab for Computer
Graphics, co-founded Environmental Systems Research Institute
(ESRI) with his wife Laura. ESRI would become in a few years
the dominate force in the GIS marketplace and create ArcInfo
and ArcView software. The first conference dealing with
GIS took place in 1970 and was organized by Roger Tomlinson
(key individual in the development of CGIS) and Duane Marble
(professor at Northwestern University and early GIS innovator).
Today, numerous conferences dealing with GIS run every year
attracting thousands of attendants. In the 1980s and 1990s,
many GIS applications underwent substantial evolution in
terms of features and analysis power. Many of these packages
were being refined by private companies who could see the
future commercial potential of this software. Some of the
popular commercial applications launched during this period
include: ArcInfo, ArcView, MapInfo, SPANS GIS, PAMAP GIS,
INTERGRAPH, and SMALLWORLD. It was also during this period
that many GIS applications moved from expensive minicomputer
workstations to personal computer hardware.
Components of GIS
A Geographic Information System (GIS) combines computer
cartography with a database management system. GIS consists
of three subsystems: (1) an input system that allows for
the collection of data to be used and analyzed for some
purpose; (2) computer hardware and software systems that
store the data, allow for data management and analysis,
and can be used to display data manipulations on a computer
monitor; and (3) an output system that generates hard copy
maps, images, and other types of output.
Two basic types of data are normally entered into a GIS.
The first type of data consists of real world phenomena
and features that have some kind of spatial dimension. Usually,
these data elements are depicted mathematically in the GIS
as either points, lines, or polygons that are referenced
geographically (or geocoded) to some type of coordinate
system. This type data is entered into the GIS by devices
like scanners, digitizers, Global Positioning Systems (GPS),
air photos, and satellite imagery. The other type of data
is sometimes referred to as an attribute. Attributes are
pieces of data that are connected or related to the points,
lines, or polygons mapped in the GIS. This attribute data
can be analyzed to determine patterns of importance. Attribute
data is entered directly into a database where it is associated
with element data.
The location of some of the earthquakes that have occurred
in the last century can be captured. The plotted data points
can be defined as elements because their main purpose is
to describe the location of the earthquakes. For each of
the earthquakes plotted on the map, the GIS also has data
on their depth. These measurements can be defined as attribute
data because they are connected to the plotted earthquake
locations. The attribute earthquake depth organized into
three categories: shallow; intermediate; and deep. This
analysis indicates a possible relationship between earthquake
depth and spatial location - deep earthquakes do not occur
at the mid-oceanic ridges.
Within the GIS database a user can enter, analyze, and manipulate
data that is associated with some spatial element in the
real world. The cartographic software of the GIS enables
one to display the geographic information at any scale or
projection and as a variety of layers which can be turned
on or off. Each layer would show some different aspect of
a place on the Earth. These layers could show things like
a road network, topography, vegetation cover, streams and
water bodies, or the distribution of annual precipitation
received. The output merges data layers for vegetation community
type, glaciers and ice fields, and water bodies (streams,
lakes, and oceans).
|
|
|
