There seems to be little indication of the human requirements in this area. And what metrics do exist, such as how much time is required to get to a point, seem artificial. Most research is in the visual representation of hierarchies, yet there are few tools to assist sophisticated access to these representations. The mapping of hierarchies has overshadowed the manipulation of them. As the data becomes more complex users require widgets to dynamically access information.
Success depends on a clear integration of mapping and manipulation.
Navigation issues are an important area to continue investigating. A good solution requires the support of an adaptive history management. Additionally many of the current solutions do not adequately exploit the underlying data. Landmarks, personality of data, neighborhood information need to be exploited to aid the user in navigation. Correlation of elements within the structure is lacking.