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Most people searching the Web these days use search engines, software that indexes and stores billions of Web pages into a huge virtual database that can, in turn, be searched by a user entering words, names, or phrases. To many users, a search engine is like a card catalogue for the Internet. When a user conducts a search, the search engine sifts through the index ("card catalogue") to find matches to the keywords that they have entered. The software then organizes the search results into a list, ranking them in an order from most to least relevant.
A variety of factors affect when, if, and how search engines index the Web pages they visit, and the criteria they use to rank the results for a given search. EPA data owners and managers can improve the ranking of their pages by incorporating the following techniques. The improved search results will likely make it easier for targeted audiences to find your pages.
How Search Engines Index & Rank Web Sites
Search engines determine relevance by following a set of rules, based mainly on search terms in the documents. Pages with keywords located in the title tag are assumed to be more relevant to the topic than most other relevance criteria. Although titles do not appear on the actual page when viewed through a browser, they are too important from a relevance ranking standpoint to be overlooked.
After the page title, search engines will check to see if keywords are located near the top of the page, such as in a page heading (such as enclosed in <H1> tags) or in the first few paragraphs of text. The assumption is that any page relevant to the topic will likely mention that topic at or near the beginning.
Frequency is the other major factor in how search engines determine relevancy. A search engine will analyze how often keywords appear in relation to other words for a given Web page. Those with a higher frequency are often deemed more relevant by the search engine than other Web pages when building its search results list.
Using Meta Tags
A number of search agents index the contents of meta tags, an optional HTML tag, unseen by the browser, but viewable from within the page's source code. The meta tags go inside the header tags, so that everything looks like this:
<HEAD>
<TITLE>US Environmental Protection Agency Home Page</TITLE>
<META name="description" content="The United States government's comprehensive information source for safeguarding the environment and protecting human health.">
<META name="keywords" content="Environmental Protection Agency, EPA, Superfund, Brownfields, Envirofacts, search by zip code">
</HEAD>
The most important tag for search engine indexing, after title, is the description tags, as shown in the example above.
Description meta tags provide a brief summary of the content of a given page. This description is subsequently displayed within a search engine's results list.
Keyword meta tags provides words and phrases for the search engine to associate with a given page. The keyword meta tag is ignored by most public search engines, due to abuse by many sites long ago, but it is important to EPA and is used by the EPA search engine.
Other Considerations
- Image Maps--A number of search agents index the full content of imagemaps, an image or graphic with one or more areas that are typically hypertext-linked to other Web pages within that site.
- Alt Tags--A number of search agents index the "alt" text associated with images. This is usually a description of the picture or image that one often sees before an image is fully loaded on a Web page.
- Link Popularity--Another factor is the number of links from other sites to an individual page. Some engines then use this information as a means to determine which second-level pages they will include in the index.
- Frequent Updates--A final prominent factor is frequent page updates. A number of search engines are programmed to "learn" how often pages change. A page that changes often will be visited frequently and reindexed, while those that do not will receive fewer visits.
Registering Your Web Pages
Once you incorporate these techniques, the final step is to register your area's home page and other major entry points with search engines. All the popular search engines offer free registration through the completion of a simple form.
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