## 5.5 Cognitive and post-structural arguments

The interpretation of the results of cost-surface and viewshed analyses has taken two, partly complementary, routes. Wheatley and Gillings (2000, 4) suggested that visibility could be considered either as an abstract consequence of the environment or as a human perceptual act. Theoretically, human perception in GIS studies has been defined according to Gibson's concept of affordance. Perception is thus defined by the ableness of the perceiver and the restrictions of the environment during the visual act (e.g. Gillings and Goodrick 1996; Llobera 1996; Wheatley and Gillings 2000; Llobera 2003). In practice, only the latter is considered.

It is not possible to apply or understand interpretations of visibility analyses without further philosophical and theoretical considerations. The permanent features of landscapes allow the analogy of a possible similar perception in past and present. However, the applicability of this analogy requires the assumption of universality of perception (Brück 1998). In the case of GIS this universality has to be broadened to include computer-aided, modelled perception. The fact that a computer perceives can lead to the conclusion that the act is done by proxy (Whitley, this volume).

The permanent nature of landmarks allows the application of Bourdieu's (1977) and Giddens' (1984) ideas of cultural construction of space to the interpretation of visible areas. I have discussed the possibilities of this elsewhere (Rajala 2003) and continue this discussion in section 6.2. A preference of cognitive or post-structural thinking is behind the choice of principles that guide the interpretation process and create archaeological understanding.