When developing expert systems for technical domains, spatial information often has to be considered. Due to the nature of space in technical domains, special representations and special processing methods for spatial problems are needed. Recent work in this area includes some interesting approaches. Most of them handle this complex area very pragmatically—dependent on their domain. In this contribution, we take a more formal approach and direct our attention towards the definition of a set of domain-independent spatial relations, from which more complex relations can be constructed. Just four primitive relations are needed. They are sufficient for describing the whole set of spatial relations between two rectangles parallel to the axes of the coordinate system. In order to show the relevance of this approach to real-world applications, we use the cabin layout of an AIRBUS A340 as an example.