We present four human behavioral experiments to address the question of intuitive granularities in fundamental spatial relations as they can be found in formal spatial calculi that focus on invariant characteristics under certain (especially topological) transformations. Of particular interest to this article is the concept of two spatially extended entities overlapping each other. The overlap concept has been extensively treated in Galton's mode of overlap calculus . In the first two experiments, we used a category construction task to calibrate this calculus against behavioral data and found that participants adopted a very coarse view on the concept of overlap, only distinguishing between three general relations: proper part, overlap, and non-overlap. In the following two experiments, we changed the instructions to explicitly address the possibility that humans could be swayed to adopt a more detailed level of granularity, that is, we encouraged them to create as many meaningful groups as possible. The results show that the three relations identified earlier (overlap, non-overlap, and proper part) are very robust and a natural level of granularity across all four experiments but that contextual factors gain more influence at finer levels of granularity.