One important issue in developing assistive navigation systems for people with disability is the accuracy and relevancy of the systems’ knowledge bases from the perspective of these special user groups. The theory of affordances coupled with computer-based simulation offers a solution for automating the extraction of the relevant information from readily available sources - architectural floor plans. Simulation of movement in a wheelchair can be used to compute the accessible space of an indoor environment by comparing the degree of match between geometrical demands of navigation and the relevant physical properties of the environment. We also investigate what constitutes the right level of representation of the environment and adopt the grid graph model as suitable both for accessibility computation and for deriving higher-level networks of places and their connections that facilitate orientation and user-system interaction. Key words: building accessibility; affordance simulati...