Networks of sensors and simulation models of the physical environment have been implemented separately, often using agent-based methodologies. Some work has been done in providing real-time integration of sensors and models. Given the distributed nature of geospatial processes, the use of software agents for representation, communication, and analysis seems to be a reasonable basis for such integration. An agent-based system that senses the actual presence of mobile organisms in a spatial environment and simultaneously represents simulated organisms individually in a model of that environment is described here.