TREE NAVIGATION
Tree navigation allows for access to a hierarchical structure. This type of mechanism is commonly seen in operating systems to navigate file folders, e.g., in Microsoft Windows Explorer. It is invariably shown as a vertical arrangement of folders, terms, or nodes of some hierarchy. Often there are small plus and minus icons to open and close nodes of the hierarchy, or there may be small arrows that point right and down for closed and open, respectively.
Opening and closing the tree on the Web can be problematic if a page reload is involved. If a user has scrolled down and the page refreshes to the top after expanding a node, the open node may be located offscreen. Avoid page reloads with tree navigation on the Web if you can. If page refreshes are needed, scroll the page automatically to the position the user last left it.
Safari Books Online (http://search.safaribooksonline.com) uses a tree navigation to access book categories. This appears on the lower-left side of the store's main page, seen in the closeup in Figure 3-15.
Figure 3-15. Tree navigation on Safari Books Online
This tree is simple and effective, but there is a distinct interaction problem: after opening a branch, the page reloads back to the top, not to the point where a category was opened. Trying to get to the section on the programming language C, for instance, requires scrolling several times to re-access ...
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