A fundamental concept with multimedia systems is that of 'seamless integration' of various media types. The concept is analysed in the context of spatial planning environments. After traditional uses of various media and the relationships between those media have been surveyed, the implications of media integration for the planning and design process are examined. The benefits are described implicitly, enabling a single plan to be viewed from different perspectives. At the technological level, this is related to the integration of design-planning teams and the integration of different phases of the design and planning cycle. The state of the art in multimedia integration is described and it is shown that a technological perspective on integration is restrictive because of its neglect of human factors. A system is proposed which might deliver the flexibility required by contemporary design-planning teams.