Environmental management is a scientifically and procedurally complex task requiring the involvement of a range of disciplines. Increasingly this process is being rendered more tractable through the application of geographic information systems (GIS) technology. When such systems are effectively integrated with biophysical modelling software a spatial decision support system can be achieved. The outputs of such a system are often in the form of visualizations, i.e. a sequence of graphics (perhaps of unit length and possibly including text), designed to meet specific communication objectives. This paper describes general requirements for the design of visualizations.