ABSTRACT
Various researchers in the GIS community show confusion between the concepts of fuzzy and probable models of uncertainty and particularly how these may be applied to modelling spatial phenomena. This chapter will use the viewshed function, familiar to many users of both raster and vector GIS, to exemplify the distinction. At the same time, a mathematical formalization is presented for some of the empirical methods employed by landscape architects in landscape evaluation and aesthetics, and results of significance to visual impact assessment are outlined.
