Feature Article (Pub: November 06) The Google Supplemental Index by Paul Rudman

Depending on who's statistics you believe, Google deals with anything from 60% to 90%+ of all search engine traffic, so whichever way you look at it getting high rankings in the Google listings for important, relevant and searched on phrases will generate a great deal of traffic - and hopefully business - for you.

However, in recent years a phenomenon known as the Supplemental Index has reared its head, with Google causing problems for website owners who keep an eye on how their site is doing in the Google index, and seek to gain traffic from the engine.

So what exactly is the Google Supplemental Index?

As with most quirks that are identified with search engines, they don't actively come out and issue a statement declaring "The Supplemental Index is xyz", but through trial and error the common consensus is that the Supplemental Index is a database of web pages that have been indexed by Google and categorised as being 'supplemental' through meeting a series of undesirable criteria.

The reason I say undesirable is that having content on the Supplemental Index isn't a good thing. It means that Google doesn't place much value on that particular web page, and as a result a supplemental page will never be returned in a search engine result - unless that search is done only on the single specific domain that the page abides in (an example of this type of search is if you type in "site:www.yourdomain.com" into Google, as only pages from that site will be returned).

What makes Google add pages to the Supplemental Index?

If some or most of the content on your site is within the Supplemental Index, then naturally you'd want to know how it ended up there and how you get it out. There are no hard and fast rules as to what gets content to be categorised as supplemental, but the following are regarded as being very strong candidates for inclusion:

Duplicated content
If a high degree of the code and content on your pages is the same then Google is likely to regard the information as less important and categorise it as supplemental. This is a common problem on e-commerce websites.
Canonical URL issues
An often overlooked issue is the potential risk of duplication that can occur if the URL http://yourdomain.com does not point to the URL http://www.yourdomain.com, as Google and the other search engines may view one site as a duplicate of the other

How can I prevent my pages from being considered supplemental?

There are several steps to follow in order for you to de-list your content and get it back within the regular Google database of indexed pages. There is no defined time period for getting your content out of supplemental status, but the following points are all best practice content and coding techniques which can help:

Create unique meta data for each page on your site
Meta data is a group of tags that sit within the <head> section of a page. The <head> section contains information and commands for browsers, servers, and search engine spiders, so be sure that you have unique <title></title>, <meta name="description" content="Put your unique description here." />, and <meta name="keywords" content="put your unique keywords here." /> tag contents.
Make sure each page on your site has unique copy
The common problem with e-commerce sites is that to the user, each category and product group will look clearly different and unique, because of the content of the product image. However, search engines cannot read image contents (excepting the image alt attribute), and so when they analyse the code they may determine that one product page is indistinguishable from another, and therefore duplicate. The way around this is to make sure there is a unique product description on the page, that is at least two paragraphs - or 50-60 words - long (and therefore too long to be simply added to the alt attribute), to make sure the copy is unique.
Cross-link pages
Try and cross-link from other pages as frequently as possible, so that you don't have a situation where you have 500 pages on your site that only have 1 internal link pointing to them. Google is far more likely to regard a page as being un-important and worthy of supplemental status if it believes you don't value it yourself.
Use a 'permanent' 301 redirect
Use 301 redirects to point http://yourdomain.com to http://www.yourdomain.com: Do not use a 302 redirect as search engines do not understand or follow this command. If you are interested in learning how you can create a 301 redirect, just type it in Google, there are plenty of helpful guides about.

The main thing if you find yourself with site content in the Supplemental Index is not to worry. Just adopt some plans to build on the unique content, make sure your meta data is unique on each page and the potential canonical duplication penalty is resolved, and just keep working at it; you'll get out of the Supplemental Index and into the main Google database of pages eventually.

Paul Rudman is the director and head of optimisation at CommerceTuned, he's been involved in developing search strategies and search engine optimisation for 7 years.

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