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A-Z Web Site Indexes Explained

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A-Z indexes are far more accurate than search engines for searching the content of a web site or intranet. For the value it can bring to your site, an A-Z index may be worth the additional cost. Heather Hedden covers the details.
Originally Published December 6, 2004 on Sitepoint.com
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Prepared by the same professional indexers who index books, A–Z web site indexes follow the same style as indexes at the back of books, including multiple levels of entries and cross-references; however, instead of printed page numbers to look up, the index entries are hyperlinked to the appropriate web pages or anchors within web pages. Following are some of the benefits of adding an A–Z index to a site:

  • Compared with onsite search engines, human-created A–Z indexes are more accurate in their retrieval of the appropriate web pages. The index points to concepts and topics no matter how they're worded, and not just to exact matches to specific words.
  • A browseable index is more user-friendly than a search engine and can keep a visitor longer at a web site.
  • The links in an A–Z index can enhance the web site's search engine optimization ranking.
  • The browseable nature of the A–Z index helps to solve problems arising from incorrect or variant spellings and singular versus plural usages.

Of course, some costs are involved. A web site index needs to be created to take the changing nature of the site into consideration, and the index will have to be maintained.

How Alphabetical Indexes Work

An A–Z index offers an alphabetical list of "entry point" topics through which the user can browse. In an index at the back of a book or manual, the entries are followed by page numbers. On a web site, the entry points are hyperlinked to the appropriate pages, and often to named anchors within web pages for an even greater level of detail in indexing.

A web A–Z index is typically a single long HTML page, although it can be broken into separate pages for each letter of the alphabet. The top of each page typically includes a horizontal list of the letters of the alphabet (see Figures 1 and 2 for samples). The user selects the appropriate letter in this list to jump to the corresponding section of the alphabetical index.

As with book indexes, a site index may contain multiple entries worded differently but pointing to the same page or anchor. Such double posting is used to cover all the ways that a user may think a topic is listed, including synonyms (cars and automobiles) and different word orders of phrases (automobile engines and engines, automobile). A main entry may include a second level of terms, called subentries, that are indented under the main entry.

A–Z indexes are created not by machines, but by humans who take care to add index entries only to pages on which good information about the topic appears. In this way, the indexing of topic words mentioned in passing or out of context is avoided, boosting the overall relevance and quality of the index itself.

A list of some examples of A–Z indexes can be found at the web site of the Web Indexing Special Interest Group (SIG). The page Web Index Examples has indexes done by SIG members.

Better Than Search Engines

Why don't we see more A–Z indexes? The simplest answer is that the big competitor to A–Z indexes—site search engines—are usually cheaper (or maybe even free) to implement. But, in the end, you get what you pay for:

  • Site search engines may not retrieve enough (or any) pages. Web search engines usually produce satisfactory results in the quantity of pages, as users generally want some information about a subject, and typically can find it on some of the numerous pages retrieved. If many good pages are missed by the search engine, the user usually doesn't notice or care, because enough other good pages are found. Within a web site, however, the number of pages is relatively small, so a simple search engine might not yield enough (or any) results, even if good pages are available on the desired subject. This is most likely to occur because the search subject that the user enters is worded or spelled differently than references to that topic within page text.
  • Site search engines may retrieve too many irrelevant pages. Whole-web search engines usually produce satisfactory results in the quality of articles, because the major search engine companies have developed complicated criteria and algorithms for retrieval and ranking of pages. Off-the-shelf search engines used within a site are not so sophisticated. They often retrieve pages that include a mere passing mention of the search term, but don't really focus on the subject at all.
  • Search engines often cannot meet the higher demands that searchers have for searches within a site. Searchers of a site may want all the information the site has to offer on a given topic, whereas searchers of the entire web only want—and expect—some information on a topic. Searchers of a site may also want to find the information more quickly if they're looking at a number of sites simultaneously.

In the end, the quality of the search engine results reflects the sophistication of the search string entered by the user, which cannot be controlled by the site. In the A–Z index, on the other hand, the quality of the results reflects the sophistication of the indexer.

Additional Advantages of A–Z Indexes

In addition to superior search accuracy, A–Z indexes offer other benefits:

  • The large number of well-labeled internal links that make up an A–Z index increases the search engine optimization rating of the linked pages and, consequently, that of the entire site.
  • The absence of irrelevant pages retrieved make index searching efficient, enhancing the usability of the web site.
  • The ability to browse the index enables users to digress and explore other topics that catch their attention, keeping them on the site longer. In other words, indexes can enhance the "stickiness" of the site.
  • A–Z indexes can be implemented effectively on web sites that are too small to work with site search engines, such as sites in the range of 20–50 pages.

No More Costly Than Customized Search Engines

Of course, basic site search engines can be made more effective with tinkering. They can be customized to search only meta tags, and meta tags can then be carefully written for each page. Searches can be restricted to certain pages and/or zones within pages. Results can be tailored to display keywords in context. But all this customization requires the expertise of web developers, whose time is not cheap. And the improvement in the search engine's capabilities still can never match those of a carefully crafted A–Z index.

Creating an A–Z index, on the other hand, is a straightforward editorial task that can be completed by a freelance indexer. Indexers can provide an accurate price quote for the job before beginning, based on the average number of words per indexable page or the number of entries in the index. Depending on the size of the web site or intranet, you can expect an A–Z index to cost $200–1,000.

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