Finding useful information on the World Wide Web is something many of us take for granted. According to the Internet research firm Netcraft, there are nearly 150,000,000 active Web sites on the Internet today [source: Netcraft]. The task of sifting through all those sites to find helpful information is monumental. That's why search engines use complex algorithms -- mathematical instructions that tell computers how to complete assigned tasks.
Google's algorithm does the work for you by searching out Web pages that contain the keywords you used to search, then assigning a rank to each page based on several factors, including how many times the keywords appear on the page. Higher ranked pages appear further up in Google's search engine results page (SERP), meaning that the best links relating to your search query are theoretically the first ones Google lists.
For Web page administrators, being listed prominently on Google can result in a big boost in site traffic and visibility. In 2007, Google surpassed Microsoft as the most visited site on the Web [source: The San Francisco Chronicle]. With that much traffic, getting a good spot on a Google SERP could mean a huge boost in the number of site visitors.
Google's keyword search function is similar to other search engines. Automated programs called spiders or crawlers travel the Web, moving from link to link and building up an index page that includes certain keywords. Google references this index when a user enters a search query. The search engine lists the pages containing the same keywords in the user's search terms. Google's spiders may also have some more advanced functions, such as being able to determine the difference between Web pages with actual content and redirect sites -- pages that exist only to redirect traffic to a different Web page.
Keyword placement plays a part in how Google finds sites. Google looks for keywords throughout each Web page, but some sections are more important than others. Including the keyword in the Web page's title is a good idea, for example. Google also searches for keywords in headings. Headings come in a range of sizes, and keywords in larger headings are more valuable than if they are in smaller headings. Keyword dispersal is also important. Webmasters should avoid overusing keywords, but many people recommend using them regularly throughout a page.
Google's PageRank System
The Google algorithm's most important feature is arguably the PageRank system, a patented automated process that determines where each search result appears on Google's search engine return page. Most users tend to concentrate on the first few search results, so getting a spot at the top of the list usually means more user traffic. So how does Google determine search results standings? Many people have taken a stab at figuring out the exact formula, but Google keeps the official algorithm a secret. What we do know is this:
- PageRank assigns a rank or score to every search result. The higher the page's score, the further up the search results list it will appear.
- Scores are partially determined by the number of other Web pages that link to the target page. Each link is counted as a vote for the target. This logic is that pages with high-quality content will be linked to more often than mediocre pages.
- Not all votes are equal. Votes from a high-ranking Web page count more than votes from low-ranking sites. You can't really boost one Web page's rank by making a bunch of empty Web sites linking back to the target page.
- The more links a Web page sends out, the more diluted its voting power becomes. In other words, if a high-ranking page links to hundreds of other pages, each vote won't count as much as it would if the page only linked to a few sites.
- Other factors that might affect scoring include how long the site has been around, the strength of the domain name, how and where the keywords appear on the site and the age of the links going to and from the site. Google tends to place more value on sites that have been around for a while.
- Some people claim that Google uses a group of human testers to evaluate search returns, manually sorting through results to handpick the best links. Google denies this and says that while it does employ a network of people to test updated search formulas, it doesn't rely on human beings to sort and rank search results.
