426 GEOGRAPHIC INFORMATION SYSTEMS
to this address and the map indicates that these streets are
one-way in given directions, they are able to plan their route
accordingly. A GIS may perform the same operation because
it has the same information—that 6th and 7th intersect
Central Avenue, the directed flow of traffic on these streets,
and the distinction of areas on the left and right side of a line.
This case is an example of what is called a “vector format”
GIS, where space is represented by a two dimensional mani-
fold of polygons (city blocks) which are bounded by a set of
directed line segments (streets).
The other format by which a GIS may represent spa-
tial data is referred to as “raster format.” In this format, an
area or volume is represented by a two or three dimensional
matrix of uniform data elements, called “grid cells.” Grid
cells are the smallest areas that this type of GIS may resolve
and are artificial constructs uniform in size and shape and
are considered to have homogeneous data properties. An
example would be a Soil map represented as a series of 30
meter by 30 meter plots of ground, where each plot is con-
sidered to be one particular type of soil, or a uniform blend
of multiple soil types. An advantage of the raster format is
the ability to show gradual changes and trends over a spatial
area, because the matrix indices of the grid cell coordinates
inherently imply the topology of the GIS data set. One of the
disadvantages of the raster format is that data in the “real
world” may not conveniently break down into uniform grid
cells. Consequently, using this format involves an optimiza-
tion problem to select a grid cell resolution that adequately
represent the given data set, while minimizing the database
size. Decreasing the size of gird cells in a raster exponen-
tially increases the database size.
With the growing usage of Geographic Information
Systems, there is a corresponding need for standardization.
Standardization does not mean that all GIS databases con-
tain the same format and quality of information; instead it
provides a common terminology and format for maintainingappropriate metadata, or data about data. Currently in the
United States, the official federal standard regarding GIS is
the Spatial Data Transfer Standard, which provides a spe-
cific terminology for GIS through a set of definitions and
format for maintaining an appropriate spatial data quality
report for metadata. The importance of providing a stan-
dard, such as the SDTS, is that it provides the end user with
and ability to assess whether or not the output from a GIS
has the quality necessary to carry out further operations or
analysis.
Dueker and Kjern’s definition of a GIS is the most appropri-
ate to consider, because the successful adoption of a GIS does
not rely only on purchasing a software package. A GIS relies
on people gathering the appropriate data, which is then input
and manipulated in the GIS software environment, and which
has knowledgeable individuals interpreting and analyzing
results for their acceptability. Therefore, these elements must
be considered as part of a Geographic Information System.REFERENCESCooke, D.F., 1992, Spatial Decision Support System: Not Just Another GIS,
Geo Info Systems, May 1992, pp. 46–49.
Cowen, D.J., 1988, GIS versus CAD versus DBMS: What Are the Differ-
ences Photogrammetric Engineering and Remote Sensing, Vol. 54,
No. 11, pp. 1551–1555.
Dueker, K.J., 1987, Geographic Information Systems and Computer Aided
Mapping, APA Journal, Vol. 53, No. 3, pp. 383–390.
Joffe, B.A. and B.S. Bergstrand, 1992, Managing Engineering Drawings in
a GIS Environment, Geo Info Systems, April 1992, pp. 58–63.
Huxhold, W.E., 1991, Information in the Organization, An Introduction
to Urban Geographic Information Systems, Oxford University Press,
New York, pp. 3–24.
National Institute of Standards and Technology (NIST), 1992, Federal
Information Processing Standard Publication 173: Spatial Data Trans-
fer Standard, Part 1, U.S. Department of Commerce.TODD HEPWORTH
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