January 01, 2002
Supplemental Navigation Systems
Two Out of Three Ain't BadSupplemental navigation systems, also called remote navigation elements, give users additional, non-hierarchical ways to navigate a site. Three common supplemental navigation systems are tables of contents, indices, and site maps. How can you choose?
Rosenfeld and Morville explain why some supplemental navigation systems are better than others.
Tables of contents
Tables of contents are effective supplemental navigation systems because users recognize them from books. They work best for large sites organized hierarchically.
A good table of contents should show at least the top two levels of the site's hierarchy, preferably in a format that visually reinforces that hierarchy. Users can sidestep the hierarchy, however, by using the table of contents to navigate to any level of the site.
The best part about tables of contents is that they're easy to implement as long as you've got a solid hierarchy already. Just take titles from the first few levels of your site, arrange them in the right order, and you've got a table of contents.
Indices
Site indices are detailed, alphabetical lists of terms that have more entries and less levels of hierarchy than tables of contents. Indices, like search engines, help users who know exactly what they're looking for. And, like tables of contents, they work because users have seen them before.
Site maps
A site map graphically illustrates a Web site's architecture. They're great in theory, but Peter Morville points out that they usually don't work in practice. To help ward off pointless site maps, he's invoked three Cartography Commandments.
We can infer that Morville's fourth commandment might be "Thou shalt avoid automatically generated site maps." They wreak havoc on usability, they don't work unless a site is strictly hierarchical (few are), and are often poorly maintained. When it comes to supplemental navigation systems, you might as well stick with a table of contents or an index.
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