But what is a 404 error page? To answer this, we must first understand what a 404 error is. A 404 DNS error is commonly known as a File Not Found error. This is what you see when you type in a URL that does not exist into your browser's address bar. Usually, the server returns something akin to 404 - File Not Found. If a search engine comes across such an error, it can have a negative impact on your search engine visibility. The solution to this is the creation of a custom error page, usually named 404.htm. When this page is extant on the server, instead of a File Not Found error being returned, the 404.htm file is returned. It can be thought of as a "catch-all" page, that is displayed when no file corresponding to the file called upon in the address bar exists.
Most good seo's will implement what is known as descriptive file naming as part of a search engine optimization project. In a nutshell, descriptive file naming is simply the naming of HTML files according to the content of that file. Fore example, let's say you own a carwash in Austin, Texas. You have a page which itemizes your various services and their corresponding prices. Currently, the page is named services.htm. After search engine optimization, this page is renamed to something like austin-carwash-services.htm, utilizing a descriptive file naming methodology. The problem is that search engines may have already indexed the services.htm page, or third party (external) web sites may link to the services.htm page. Obviously, you don't want people using these links to reach a non-existent page, and likewise you don't want search engines linking to it or finding non-existent pages. The 404.htm page is also useful in the event external links or user inputs contain typographical errors.
Installing a 404.htm file on the server, and enabling custom error pages in your control panel (if necessary), solves the problem. Any user who clicks on a link to the old services.htm page reaches the 404.htm page instead of receiving a 404 DNS error. Search engines do the same thing. This ensures that no user is left stranded in "no man's land", and increases web site "stickiness".
Critical Elements of a 404 Error Page
Remembering that the 404.htm file will be encountered any time a 404 error would otherwise be returned, it is intuitive that the page must contain generic content, related to the overall theme of the site, as opposed to page-specific content. What this means is that creating a 404.htm file, in the example above, solely for the missing page services.htm, would be a mistake. For example, if you created your 404.htm file to be a mirror of the old services.htm file, if someone linked to another non-existent page of your site, for example an about us page named about.htm which has been renamed, they would land on the 404.htm page containing service information. This would likely lead to confusion on the part of the user. As such, building a 404.htm page with generic information is best practice.
A 404.htm page should hold the same "look and feel" as the rest of the site. Usually, this would mean a banner image with navigation bar, with an area for page-specific body content. Using the CSS or web site page template, create the 404.htm page to contain body text which informs the user of the non-existence of the desired page, and clearly directs the user to important areas of the web site.
So, at a minimum, the 404.htm page would contain the following:
1) Same look and feel as the rest of the site
2) Error message, such as "The page entered was not found on our server. Please try one of the links b
