Site index - to do or not to do?

I prepared a site index for my website. A site index is like a book index; an alphabetically listing of the topics contained in the website, in the users words. Site indices don’t try to contain every link but point to the content that is best suited for that term.

At this point, it is a given that all websites should have search engine functionality and a site map (a hierarchal map of the pages in a website).

But someone commented that our site doesn’t need a site index. With most websites above-the-fold real estate is at a premium and thus my site index will probably be relegated from the very-useful utility bar to the purgatory of the site footer.

Today, I read this article in Boxes & Arrows called “Improving Usability with a Website Index” by Fred Leise. Leise describes the advantages of site index as:

They offer easy scanning for finding known items, they provide entry points to content using the users’ own vocabulary and they provide access to concepts discussed, but not named, in the text.

A good search engine (and frankly many sites have crappy ones) can go a long way, but they often pull up too much information and are confined by the ability of the user to articulate – and using the correct terminology – what information they are looking for. A site map can help for browsing, but can also be overwhelming, and unless the webpage titles are very indicative and definitive they may not capture what the user is looking for.

To help with some of these problems, I compiled a thesaurus of both official and user terminology, that is built into the search engine. This helps a lot, but still requires users to be able to articulate their query and may actually increase the already too-plentiful results.

Who better than a human very familiar with a website’s content and the site’s users and their vocabulary to devise a search aid?

According to Leise they aid website usability:

Indexes, as flat lists of terms, are easily scannable. Users need only use their browser’s scroll bar to navigate through the entire index. (Large indexes often provide alphabetical anchor links at the top of the index, which take users quickly to the portion of the index they need to use.) There are no multiple levels to navigate, nor must users decide which branch of a hierarchy to click on, which often results in their missing information, they are looking for or taking longer to find it. In fact, the easy scannability of the index on a single page is an important argument against having separate pages for letter of the alphabet, whenever possible.

Okay, I’m sold on the site index, but I’d love to hear anyone else’s opinion or experience using them or developing them for their site.