Context and interaction in Zoomable User Interfaces

Zoomable User Interfaces (ZUIs) are difficult to use on large information spaces in part because they provide insufficient context. Even after a short period of navigation users no longer know where they are in the information space nor where to find the information they are looking for. We propose a temporary in-place context aid that helps users position themselves in ZUIs. This context layer is a transparent view of the context that is drawn over the users' focus of attention. A second temporary in-place aid is proposed that can be used to view already visited regions of the information space. This history layer is an overlapping transparent layer that adds a history mechanism to ZUIs. We complete these orientation aids with an additional window, a hierarchy tree, that shows users the structure of the information space and their current position within it. Context layers show users their position, history layers show them how they got there, and hierarchy trees show what information is available and where it is. ZUIs, especially those that include these new orientation aids, are difficult to use with standard interaction techniques. They provide a large number of commands which must be used frequently and on a changing image. The mouse and its buttons cannot provide a rapid access to all these commands without new interaction techniques. We propose a new type of menu, a control menu, that facilitates the use of ZUls and which we feel can also be useful in other types of applications.