Computational representation of spatial qualitiescan lead usto abetterunderstanding of how weconstruct spatial concepts. Analyses of spatial qualities can support architects in reasoning about the form of a configuration, helping them predict the consequences of a design. In this paper we present three definitions (enclosure, viewfield, continuity) that describe experiential qualities of architectural spaces. Our project aims to provide computable definitions to these qualities to describe common spatial experiences that are implicitly understood by architects. The description, using familiar terms, reveals the analytical structure of spatial qualities that is based on the geometry of the physical elements. We therefore introduce a graphic editor, Descriptor, that provides visualization of spatial qualities as the designer diagrams building elements. The system calculates perceived relationships (surrounded, visible, nearby, nearest) between a viewpoint and the architectural elements based on their geometric properties such as location and distance. The relationships are the components of the three qualities we define. We also present a use scenario to demonstrate how one might use our Descriptor system during early design. Descriptor is an attempt to formalize descriptions of the spatial qualities to help beginners understand how to make design decisions. In the future, we plan to extend the set of qualities and add detailed attributes of the physical elements to the system.