1. Introduction
Environmental impact assessment (EIA), and particularly cumulative
effects assessment (CEA), typically requires the analysis of large
complex data sets involving multiple actions, environmental
resources and their selected indicators, and impact-causing factors
associated with the spatial and temporal distribution of the actions. A
potentially useful tool in CEA is geographic information systems (GIS),
because such systems have the ability to store, manipulate, analyze
and display large sets of complex, geographically referenced data and
are therefore well suited to spatial applications of this nature and
complexity (Warner and Diab, 2002).
Layers of data are frequently used for presentation of historical to
current environmental information. Such layers can be combined or
eliminated for specific analyses or displays. Further, areas of
environmental constraint, as reflected by selected indicators, can be
easily identified. Combining various layers can be accomplished via
the assignment of different importance or vulnerability weights.
These assignments can be made via the use of a consistent weighting
scheme described by Saaty (1977). Further, relative to environmental
planning, buffers can be designated around intrusions, such as power
lines or access roads, or around sensitive areas, such as nesting
habitats (Warner and Diab, 2002).
Because the GIS tool is dynamic in that new environmental
information can be added over time and space, and the importance
weights of the layers that define protected areas can be modified, it is
particularly useful in evaluating planning options (e.g., site or route
locations). Further, GIS can be used to display the consequences of
multiple actions; thus, it is also particularly useful in undertaking CEA
in designated areas or regions. However, it should be noted that the
time required to prepare the database, the initial costs of the
hardware and software, and the data collection and conversion (to
digital format) costs can be deterrents to the application of this tool in
every CEA study.
Within recent years the application of GIS technology to the EIA
process has steadily increased. Relative to typical EIA phases, GIS can
have application, either directly or as a supporting tool, to all of them.
To illustrate, Table 1 lists specific ways in which GIS could be used in
various EIA phases (after Joao and Fonseca, 1996). In addition, GIS can
be used as a tool in follow-on impact monitoring, project management,
and adaptive management. More specifically, Eedy (1995)
described the usefulness of GISs relative to EIAs' need for: (1) data
management; (2) data overlay and analysis relative to site impact
prediction, wider area impact prediction, corridor analysis, cumulative
effects analysis, and impact audits; (3) trend analyses; (4)
integration into impact models such as chemical or radio-nuclear
dispersion and pathway models, climatic change models, and decision
analysis using the Multi- Attribute Tradeoff System; (5) habitat
analysis using the Habitat Evaluation Procedures; (6) aesthetic
resources and impact analysis; and (7) public consultation.
Development and implementation of a GIS for use in the EIA
process typically involve identification and conceptualization, planning
and design, procurement and development, installation and
operation, and review and audit (World Bank. 1995). Examples of
study situations which are conducive to the use of GISs in EIA are
shown in Table 2, while some specific illustrations of how GISs can be