The visibility of node instances in the presentation hierarchy affects the efficiency and effectiveness of an interface considerably. Users ability to see multiple levels of nodes at once gives them direct access to a variety of nodes at the same time. The quantity of node instances visible at each level also gives them access to multiple instances simultaneously. Thus, the visible depth of the presentation hierarchy and the visible breadth at each level improves users access to information.
If we examine the WebBook and Web Forager interface, node instances at all three levels are visible and accessible simultaneously. Due to space constraints, however, breadth is limited. Putting more node instances such as books and pages on the screen, results in overlaps and deteriorates visibility. Also as each one gets smaller, the readability of content decreases to a large degree. The visible breadth for a book instance however is limited due to the metaphor to only two pages at once, independent of its capacity (e.g. number of pages). For the vtwm interface, similarly all three levels are visible simultaneously. However, only a single desktop and its windows are visible at once. The breadth of a desktop node instance is also limited by the visibility of the windows. In the Elastic Windows interface, typically 5 levels of windows are visible and usable at once, above that a maximization is needed due to readability problems. Users can maximize windows at any level of the window hierarchy. The usable breadth for each window group depends on the size of the window group and readability of contents.