The objective of this paper is to propose a formalized mechanism of incremental interpretation ofa natural language discourse about the organization of architectural or urban spaces. The mechanism consists of two formal semantics, i.e., model-based semantics and dynamic semantics. The dynamic, semantics updates the models of a discourse in order to render a new proposition true as well as to keep the consistency of an already given discourse and the new proposition. This paper demonstrates that the proposed mechanism, together with a shape grammar, incrementally interprets spatial descriptions and constructs a planning layout with respect to the descriptions.