You may have two or more pages with the same content, but different URLs. Perhaps one is an old page you no longer wish to use as a URL, but it's listed in the search engines.
Eliminating duplicate content can improve your rankings by concentrating PageRanks and search engine rankings on one page of content.
If you cannot delete duplicate content because it has valid links, you can use one of the following techniques for "teaching" the search engines what the preferred page URL is:
301 Redirects
This is a server-side functionality that tells a visitor's browser that the page or URL they were seeking is no longer available, and then redirects the browser to the new URL.
For example, if you had a page in your Web site, http://www.example.com/berets-red-1234, and you now are selling these on a new page with a different URL, you can use a 301 Redirect to automatically redirect the visiting browser to, say, http://www.example.com/red-berets/1234. The "301" refers to a code that Web servers give to a browser. You may have seen "404" codes from time to time. This is the server telling the browser that the URL requested cannot be located or presented by the server. A 301 tells the browser that the original URL doesn't exist as a valid path, but the content it referred to is still available at a new URL address. A 301 is often called a "permanent" redirect (there are "temporary" redirects, but that's for a geekier discussion later).
If you have the ability to program 301 Redirects on your Web hosting server, do so. This is the preferred method for several reasons:
- It works better to re-point multiple domains to one primary domain.
- You don't have to have the original, old page still on the server (see Canonical Link Tag).
- 301 Redirects will actually and automatically redirect the visitor, not just the search engine spider that indexes your site.
Canonical Link Tag
In February of 2009, the major search engines (Google, Yahoo!, Bing) decided on a new link tag standard whereby you can, more or less, insert a redirect code into an existing page which will tell the search engines that the page is really a duplicate of content existing elsewhere, and that the search engine should regard the original content when indexing the Web site.
The canonical link tag is a good tool to use if you do not have the ability to program 301 Redirects on the server hosting your Web site. Many hosting companies don't allow that kind of accessibility, as programming a 301 Redirect requires modification of core preference files for the server. I know may webmasters who simply don't know how to implement them.
If you need to use canonical link tags, insert them into the <head> section of the duplicate content Web page, using this format:
<link rel="canonical" href="http://www.example.com/red-berets/1234" />
When Google, Yahoo!, Bing or Ask indexes your site and comes across this link, they will know that the content on this page is a duplicate of the link in the tag. The content doesn't have to be exactly the same, however (you're not likely to be updating an old page); the search engines will determine what to index.
Remember, canonical links as described here do not redirect the visiting browser to the new content. It only helps the search engines determine that when duplicate content is encountered, which page should be referred to in resulting search engine results.
Google Webmaster Tools
If you haven't become familiar with Google Webmaster Tools, you should do so right away. While the interface gives the impression the tools are sparse, the contrary is true. Webmaster Tools contain a nice suite of very useful applications to help you learn more about how Google sees your Web site.
Go to Google Webmaster Tools and take the time to read the "Getting Started" section. (You will need a Google gmail account to use Webmaster Tools.)
Last Word
Don't let duplicate content, especially that which may exist at old URL's or in pages you no longer wish to be public spoil your search engine optimization. Programming and managing redirects is not necessarily easy or fast, but it is necessary.
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