14.3. Hiermap

It has been widely noted in the literature that overview maps are one of the most useful means for navigation in cyberspace [Utt89]. As has been noted in chapter 11, the purpose of an overview map is at least twofold:

• Readers see where they are in the document. The context of the actual node is displayed in a fish eye view fashion [Fur86] to help in orientation.
• Readers see where they can go from the actual location. They perceive which links are starting from their location in the document.

Figure I.79 Hiermap of "Animated Algorithms"

In our overview map implementation (figure I.79), a node is represented by a box enclosing the title of the node. The map consists of many boxes, arranged hierarchically: there can be up to four rows of boxed node titles visible on the map, corresponding to the hierarchically structured hyperdocument. The current node is displayed in a highlighted box in the center of the map. A vertical line is drawn from that node to its parent node in the next higher row. The remaining boxes in each row are filled with siblings of the corresponding node. For current nodes that are in levels one through three, the result is a fish-eye view of the structure of the serial text, as viewed from the current node.

The map also allows users to "zoom in" the hierarchical node structure in a fish eye view fashion. If users wish to see the subnode structure of a particular node without actually jumping there, they can cause the display of the most prominent subnodes surrounding the particular node by clicking in the corresponding box.

In addition to displaying contextual information, the map serves another purpose: it displays nodes that have been visited. Beneath each box, a slider represents the fraction of offspring nodes that have already been read. Offspring nodes include all nodes which have that node as a parent, grandparent, etc.. Thus, the browser can tell at a glance which subjects have been explored.

Besides support for hierarchical navigation, the Gloor/Dynes hypertext engine also includes sophisticated path editing and guided tour facilities, which are described in the next chapter.