One of the most important applications of GIS is the
display and analysis of data to support the process of
environmental decision-making. A decision can be
defined as a choice between alternatives, where the
alternatives may be different actions, locations,
objects, and the like. For example, one might need to
choose which is the best location for a hazardous
waste facility, or perhaps identify which areas will be
best suited for a new development.
Broadly, decisions can be classified into two
extensive categories – policy decisions and resource
allocation decisions. Resource allocation decisions,
as the name suggests, are concerned with control
over the direct use of resources to achieve a
particular goal. Ultimately, policy decisions have a
similar aim. However, they do so by establishing
legislative instruments that are intended to influence
the resource allocation decisions of others. Thus, for
example, a government body might reduce taxes on
land allocated to a particular crop as an incentive to
its introduction. This is clearly a policy decision; but
it is the farmer who makes the decision about
whether to allocate land to that crop or not.
To be rational, decisions will be necessarily based
on one or more criteria – measurable attributes of
the alternatives being considered, that can be
combined and evaluated in the form of a decision
rule. In some circumstances, allocation decisions can
be made on the basis of a single criterion. However,
more frequently, a variety of criteria is required. For
example, the choice between a set of waste disposal
sites might be based upon criteria such as proximity
to access roads, distance from residential and
protected lands, current land use, and so on.
This chapter focuses on the very specific problems
of spatial resource allocation decisions in the
context of multiple criteria – a process most
commonly known as multi-criteria evaluation