Google has had a tendency to interpret URLs with and without the www sub-domain prefix as two different pages. Now you can tell Google not to.

All the major search engines make use of some kind of voting system. They give web pages points for incoming links, links from popular and “trustworthy” pages giving more boost than others.

There are a large number of other factors determining the ranking of a page, but link popularity — or “PageRank” as Google calls it — is definitely an important one.

This is why you, as a site owner, would rather not see this effect diluted. That happens, however, often for the most silly reasons.

www.pandia.com does not equal pandia.com

For instance: Most sites will use the www prefix as part of their web sites address or URL.

Hence www.website.com will lead to the home page of the web site. However, this “subdomain” is in no way obligatory, which is why most web servers are configured in such a way that entering website.com in the browser address field (i.e. without the www) will do the same trick.

The problem with this is that sites linking to your site may use different URLs in their links to you. One may link to www.yoursite.com/index.html, the other to yoursite.com/index.html.

To you this is the same. To the search engine, however, this may be interpreted to mean that there exist two different (but identical) web pages. Because of this some of the PageRank or points go to the www version of the page, the rest to the non-www version. You don’t want that.

The 301 redirect

Previously, the normal way of solving this problem has been to use a so-called 301 redirect, which is a command you put into your .htaccess file (a server configuration file). See Pandia’s article How to rename or move files without loosing your search engine ranking: the 301 redirect for more information.

It is not hard to do so, but you do have to know something about web servers to make it work.

Google preferred domain

Google has now added an easier to use preferred domain function to its new Webmaster Central.

The Webmaster Central contains a selection of tools and services for webmasters who want to see their pages indexed by Google. See Google and Yahoo! give webmasters a helping hand for more information about the Webmaster Central.

You have to sign up as a user of Google Sitemaps to make use of this feature (using, for instance, a free Gmail email address), but you do not have to submit a sitemap to tell Google to index all pages with or without the www.

As the Planet Ocean Search Engine News newsletter puts it:

While it’s actually too early to tell, we’re optimistic that this will solve those pesky ole duplicate content and PageRank dilution issues that Google’s been having as a result of canonical deficiencies.

In order to be 100 percent sure, however, and in order to cover all the search engines, a 301 redirect continues to be the safest bet.