A structural system model of a spatially distributed system embodies system dynamics as well as statics, explicitly depicts the various states of system operation, and includes probabilistic as well as deterministic features of operation. In this context, a locational decision is an allocation of resources within an operating system. Particularly important to the recently developed hypercube queueing model is state dependent interaction among facilities (mobile servers) that precludes application of many traditional locational theories. Recent work outlined in the paper includes a generalization of the N-median problem to congested facilities, optimal dispatching of facilities, districting (sectoring), consideration of quality of locational information, and short-term repositioning of facilities. Recent implementations of the model are also discussed. Figures, formulas, and 45 references are provided. (Author abstract modified)