Database Reference
In-Depth Information
the need to address GI in a common way became more clearly recognized, leading
to the development of commercial off-the-shelf general-purpose GIS in the 1970s.
Larger national mapping agencies, such as the U.S. Geological Survey (USGS),
Ordnance Survey of Great Britain, and Institut Geographique National (IGN) France
also recognized that computer systems could be used to help the map production
process. The systems they produced were not strictly GIS since they were designed
to manage and edit map data for cartographic purposes. Nevertheless, there were
obvious similarities between systems designed to perform analysis and those with
more cartographic intentions. What was common to all these systems was the ability
to manage, manipulate, and index geometry and to a lesser extent topology.
By the 1980s, commercial GIS were emerging, with companies such as ESRI
(Environmental Systems Research Institute, Inc.), which launched ARC/INFO in
1982, and competitors such as Integraph, CARIS, and ERDAS also developing com-
mercial GIS software in the early 1980s. In 1982, there also was the emergence of
GRASS (Geographic Resources Analysis Support System) GIS, a public domain
GIS. All these GIS were hosted either on specialist hardware or on UNIX-based
workstations such as SUN and Apollo or other minicomputers, such as the DEC
(Digital Equipment Corporation) VAX ranges. In all cases, the solutions were
extremely expensive, limiting their market penetration and resulting in the develop-
ment of GIS specialist groups within organizations.
GIS were also only used in specialist areas. At their simplest, they were used
to digitize mapping, sometimes performing transformations between different map
projection systems. Other uses were GI visualization, for example, to show the dis-
tribution of forestry in an area, perhaps differentiating between different types of
forestry; and spatial calculation, for example, to estimate area coverage by forest
type. More sophisticated still, GIS enabled organizations to perform analysis such
as determining objects within a certain distance of another object or to answer ques-
tions like “How many sightings of a particular species have occurred within 500 m of
a river?” To provide such capabilities, GIS needed to support a number of core func-
tions, all of which were present in these early systems. These core functions included
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Representing geographic objects in terms of simple geometries: points,
lines, and polygons
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Representing GI as a raster (an array of data points representing discrete values)
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Associating other data to these geometric objects
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Describing geometry in terms of one of a number of coordinate systems
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Indexing the geometry to allow selection based on position
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Performing basic spatial analysis, such as identifying objects within another
object, objects that are touching or overlapping, and objects within a given
distance of other objects
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Visualizing GI, typically as a map display or tabulation
By this time, the idea of GIS layers had also been established—essentially a means
to organize data in a number of layers that could be overlaid on top of each other to
visualize the information. The layer concept also allowed the division of information
into categories, as a layer's content was determined by geometry type and type of
