A dynamical systems approach for modeling changing spatial environments is formalised. The formalisation adheres to the representational and computational semantics of situation calculus and includes a systematic account of all aspects necessary to implement a domain-independent qualitative spatial theory that is applicable across diverse application areas. Foundational to the formalisation is a situation calculus based causal theory and a generalised view of qualitative spatial calculi that encompass one or more spatial domains. Furthermore, aspects considered inherent to dynamic spatial systems are also accounted for and the relevant computational tasks addressed by the proposed formalisation are stated explicitly.