by: Andy Hagans
Hilltop is one of the major concepts underpinning Google's search algorithm, yet its workings and implications are often misunderstood. After the infamous Florida Update, many webmasters were aghast as their rankings plummeted; and again, when the mysterious "sandbox" was implemented, some webmasters could not get a Web site to rank well, period. Part of the reason that some Web sites get shuffled out of the SERPs when new algorithmic features are implemented is that those sites never gained authority in the eyes of the search enginesthat is, they were not sufficiently meshed into their local topical communities.
This concept of authority was one pioneered in a paper titled "Hilltop: A Search Engine based on Expert Documents," written by Krishna Bharat and George A. Mihaila. The full text is available online at http://www.cs.toronto.edu/~georgem/hilltop/.
(Note: Google has obviously not implemented Hilltop in its pure form, but rather uses the principles of topical communities and authority in its algorithm. Likewise, other search engines such as MSN and Yahoo! are not using Hilltop per se, but rather similar algorithmic features. Thus when I mention 'Hilltop' I am referring to not just the specific paper published by Bharat and Mihaila, but also to the fundamental theory upon which any authority-based link popularity algorithm is based. This theory applies to Topic-Sensitive PageRank, etc.)
The Basics of Hilltop
Google's PageRank formula revolutionized search, but it has a major flaw: it gives each page an absolute measure of importance. Recognizing that a page's importance should be interpreted in light of a given query topic, the Hilltop formula uses the link structure of the topical community related to the query topic when determining relevance.
For a given topic query, some pages are considered to be "expert documents," and others are "authorities." A page is an expert document if it "is about a certain topic and has links to many non-affiliated pages on that topic" (this type of page is also sometimes called a hub). A page is an authority "if and only if some of the best experts on the query topic point to it." To summarize: hubs link to authorities; authorities are linked to by hubs.
The Challenge for New Web Sites
The nature of the World Wide Web dictates that it will take time for a new Web site to get links from within its topical community. Many hubs such as resource lists or niche directories are only updated periodically with new links. Still others are static pages that will never be changed.
Then there is the "human factor." It takes time for a Web site to be recognized as valuable, and for webmasters to trust it enough to link to it. Older authority sites and hubs also tend to link to other older authority sites, creating a sort of self-perpetuating authority set (Mike Grehan refers to this phenomenon in his article "Filthy Linking Rich," available online at http://www.e-marketing-news.co.uk/Oct04/RichLinking.html). This all adds up to the fact that it is very hard to make a new Web site an authority in the eyes of the search engine, which begs the question: How can a new Web site become entrenched in its topical neighborhood more quickly?
Break Into Your Topical Neighborhood
To make your Web site an authority, you should first seek to obtain links from topical hubs. Obvious hubs might include any niche directories or resource pages about your Web site's topic.
One way to find less obvious hubs is to do a backlink search on authority sites in your topical community. Finding authority sites is easythey are the sites that rank highly for a search for that topic. Once you find an authority, search "link:http://www.theirsite.com." Go through the backlinks, and find pages that link out to multiple sites within your topic; a page that links out to multiple authority sites is probably considered a hub by a search engine.
Aside from hubs, it can be quite helpful to get links from the authority sites themselves. I have seen many Web sites get a significant boost after obtaining just one link from a top authority. It is implied that an authority site will link out less than will a hub, and therefore it is possible that these links are even more valuable in terms of rankings.
Obtaining links from quality hubs and authorities is easier said than done. One can however use certain methods to get links quickly. These methods include but are not limited to: offering to swap links; submitting a relevant, well-written press release; submitting a relevant, well-written article with your Web site's URL hyperlinked and embedded in the copy; offering to buy or rent a links; and, of course, writing a lot of great content (it will get noticed, sooner or later!).
Conclusion
Obtaining links from reputable sources within your Web site's topical community is necessary in order for that site to be ranked highly in today's search engine algorithms. Getting your Web site entrenched within its topical community would be a good idea anyway, even if search engines did not existwhich is a pretty good litmus test for a strong, long-term SEO method.