Geographic visualisation systems (GVIS) and geographic information systems (GIS) now serve an important role in science, allowing researchers to study many problems involving spatial data. Both of these tools encourage interaction between the system user and the data being displayed and manipulated and therefore the user interfaces for GIS and GVIS are critical. In relation to GIS, Frank (1993) states that the user interface is the most important single part of the system. He is highlighting the fact that the user interface is usually the only part of the system that the user has direct contact with (especially the novice or basic user) and that its design is thus crucial to the success of a GIS. In this chapter an approach for thinking about interfaces is described. The description of this approach and how it relates to GIS will lead to an extended discussion about the use of metaphor in user interface design and how it applies to systems for geographic analysis.