The ` Egg - Yolk ' RepresentationOf Regions with Indeterminate

The paper proposes an approach to representing and reasoning about spatial regions with undetermined boundaries, using an adaptation of`RCC-theory', a region-based system for representing qualitative spatial relations developed over the last few years (Randell, Cui and Cohn 1992, Cohn, Randell and Cui 1994). The approach proposed is referred to as thèegg-yolk' representation: a region with undetermined boundaries (a `vague region') is represented by a pair of concentric regions with deter-minate boundaries (`crisp regions'), which provide limits (not necessarily the tightest limits possible) on the range of indeterminacy.