Specifically, by considering criteria as
expressions of membership in fuzzy sets (a specific instance of fuzzy measures) the
weighted linear combination aggregation process common to raster systems is seen to lie
along a continuum of operators mid-way between the hard intersection and union operators
typically associated with Boolean overlay in vector systems. A procedure for implementing
this continuum is reviewed, along with its implications for varying the degrees of
‘ANDORness’ and trade-off between criteria. In addition, the theoretical structure of fuzzy
measures provides a strong logic for the standardisation of criteria and the evaluation of
decision risk (the likelihood that the decision made will be incorrect).