3 External ranking factors

3.1 Why inbound links to sites are taken into account
   As you can see from the previous section, many factors influencing the ranking process are under the control of webmasters. If these were the only factors then it would be impossible for search engines to distinguish between a genuine high-quality document and a page created specifically to achieve high search ranking but containing no useful information. For this reason, an analysis of inbound links to the page being evaluated is one of the key factors in page ranking. This is the only factor that is not controlled by the site owner.

   It makes sense to assume that interesting sites will have more inbound links. This is because owners of other sites on the Internet will tend to have published links to a site if they think it is a worthwhile resource. The search engine will use this inbound link criterion in its evaluation of document significance.

   Therefore, two main factors influence how pages are stored by the search engine and sorted for display in search results:

    - Relevance, as described in the previous section on internal ranking factors.

    - Number and quality of inbound links, also known as link citation, link popularity or citation index. This will be described in the next section.

3.2 Link importance (citation index, link popularity)
   You can easily see that simply counting the number of inbound links does not give us enough information to evaluate a site. It is obvious that a link from www.microsoft.com should mean much more than a link from some homepage like www.hostingcompany.com/~myhomepage.html. You have to take into account link importance as well as number of links.

   Search engines use the notion of citation index to evaluate the number and quality of inbound links to a site. Citation index is a numeric estimate of the popularity of a resource expressed as an absolute value representing page importance. Each search engine uses its own algorithms to estimate a page citation index. As a rule, these values are not published.

   As well as the absolute citation index value, a scaled citation index is sometimes used. This relative value indicates the popularity of a page relative to the popularity of other pages on the Internet. You will find a detailed description of citation indexes and the algorithms used for their estimation in the next sections.

3.3 Link text (anchor text)
   The link text of any inbound site link is vitally important in search result ranking. The anchor (or link) text is the text between the HTML tags «A» and «/A» and is displayed as the text that you click in a browser to go to a new page. If the link text contains appropriate keywords, the search engine regards it as an additional and highly significant recommendation that the site actually contains valuable information relevant to the search query.

3.4 Relevance of referring pages
   As well as link text, search engines also take into account the overall information content of each referring page.

   Example: Suppose we are using seo to promote a car sales resource. In this case a link from a site about car repairs will have much more importance that a similar link from a site about gardening. The first link is published on a resource having a similar topic so it will be more important for search engines.

3.5 Google PageRank – theoretical basics
   The Google company was the first company to patent the system of taking into account inbound links. The algorithm was named PageRank. In this section, we will describe this algorithm and how it can influence search result ranking.

   PageRank is estimated separately for each web page and is determined by the PageRank (citation) of other pages referring to it. It is a kind of “virtuous circle.” The main task is to find the criterion that determines page importance. In the case of PageRank, it is the possible frequency of visits to a page.

   I shall now describe how user’s behavior when following links to surf the network is modeled. It is assumed that the user starts viewing sites from some random page. Then he or she follows links to other web resources. There is always a possibility that the user may leave a site without following any outbound link and start viewing documents from a random page. The PageRank algorithm estimates the probability of this event as 0.15 at each step. The probability that our user continues surfing by following one of the links available on the current page is therefore 0.85, assuming that all links are equal in this case. If he or she continues surfing indefinitely, popular pages will be visited many more times than the less popular pages.

   The PageRank of a specified web page is thus defined as the probability that a user may visit the web page. It follows that, the sum of probabilities for all existing web pages is exactly one because the user is assumed to be visiting at least one Internet page at any given moment.

   Since it is not always convenient to work with these probabilities the PageRank can be mathematically transformed into a more easily understood number for viewing. For instance, we are used to seeing a PageRank number between zero and ten on the Google Toolbar.

   According to the ranking model described above:
   - Each page on the Net (even if there are no inbound links to it) initially has a PageRank greater than zero, although it will be very small. There is a tiny chance that a user may accidentally navigate to it.
   - Each page that has outbound links distributes part of its PageRank to the referenced page. The PageRank contributed to these linked-to pages is inversely proportional to the total number of links on the linked-from page – the more links it has, the lower the PageRank allocated to each linked-to page.
   - PageRank A “damping factor” is applied to this process so that the total distributed page rank is reduced by 15%. This is equivalent to the probability, described above, that the user will not visit any of the linked-to pages but will navigate to an unrelated website.

   Let us now see how this PageRank process might influence the process of ranking search results. We say “might” because the pure PageRank algorithm just described has not been used in the Google algorithm for quite a while now. We will discuss a more current and sophisticated version shortly. There is nothing difficult about the PageRank influence – after the search engine finds a number of relevant documents (using internal text criteria), they can be sorted according to the PageRank since it would be logical to suppose that a document having a larger number of high-quality inbound links contains the most valuable information.

   Thus, the PageRank algorithm "pushes up" those documents that are most popular outside the search engine as well.

3.6 Google PageRank – practical use
   Currently, PageRank is not used directly in the Google algorithm. This is to be expected since pure PageRank characterizes only the number and the quality of inbound links to a site, but it completely ignores the text of links and the information content of referring pages. These factors are important in page ranking and they are taken into account in later versions of the algorithm. It is thought that the current Google ranking algorithm ranks pages according to thematic PageRank. In other words, it emphasizes the importance of links from pages with content related by similar topics or themes. The exact details of this algorithm are known only to Google developers.

   You can determine the PageRank value for any web page with the help of the Google ToolBar that shows a PageRank value within the range from 0 to 10. It should be noted that the Google ToolBar does not show the exact PageRank probability value, but the PageRank range a particular site is in. Each range (from 0 to 10) is defined according to a logarithmic scale.

   Here is an example: each page has a real PageRank value known only to Google. To derive a displayed PageRank range for their ToolBar, they use a logarithmic scale as shown in this table
          Real PR                               ToolBar PR
          1-10                                            1
          10-100                                        2
          100-1000                                    3
          1000-10.000                               4
Etc.

   This shows that the PageRank ranges displayed on the Google ToolBar are not all equal. It is easy, for example, to increase PageRank from one to two, while it is much more difficult to increase it from six to seven.

   In practice, PageRank is mainly used for two purposes:

   1. Quick check of the sites popularity. PageRank does not give exact information about referring pages, but it allows you to quickly and easily get a feel for the sites popularity level and to follow trends that may result from your seo work. You can use the following “Rule of thumb” measures for English language sites: PR 4-5 is typical for most sites with average popularity. PR 6 indicates a very popular site while PR 7 is almost unreachable for a regular webmaster. You should congratulate yourself if you manage to achieve it. PR 8, 9, 10 can only be achieved by the sites of large companies such as Microsoft, Google, etc. PageRank is also useful when exchanging links and in similar situations. You can compare the quality of the pages offered in the exchange with pages from your own site to decide if the exchange should be accepted.

   2. Evaluation of the competitiveness level for a search query is a vital part of seo work. Although PageRank is not used directly in the ranking algorithms, it allows you to indirectly evaluate relative site competitiveness for a particular query. For example, if the search engine displays sites with PageRank 6-7 in the top search results, a site with PageRank 4 is not likely to get to the top of the results list using the same search query.

   It is important to recognize that the PageRank values displayed on the Google ToolBar are recalculated only occasionally (every few months) so the Google ToolBar displays somewhat outdated information. This means that the Google search engine tracks changes in inbound links much faster than these changes are reflected on the Google ToolBar.

3.7 Increasing link popularity
3.7.1 Submitting to general purpose directories
   On the Internet, many directories contain links to other network resources grouped by topics. The process of adding your site information to them is called submission.

   Such directories can be paid or free of charge, they may require a backlink from your site or they may have no such requirement. The number of visitors to these directories is not large so they will not send a significant number to your site. However, search engines count links from these directories and this may enhance your sites search result placement.

   Important! Only those directories that publish a direct link to your site are worthwhile from a seo point of view. Script driven directories are almost useless. This point deserves a more detailed explanation. There are two methods for publishing a link. A direct link is published as a standard HTML construction («A href=...», etc.). Alternatively, links can be published with the help of various scripts, redirects and so on. Search engines understand only those links that are specified directly in HTML code. That is why the seo value of a directory that does not publish a direct link to your site is close to zero.

   You should not submit your site to FFA (free-for-all) directories. Such directories automatically publish links related to any search topic and are ignored by search engines. The only thing an FFA directory entry will give you is an increase in spam sent to your published e-mail address. Actually, this is the main purpose of FFA directories.

   Be wary of promises from various programs and seo services that submit your resource to hundreds of thousands of search engines and directories. There are no more than a hundred or so genuinely useful directories on the Net – this is the number to take seriously and professional seo submission services work with this number of directories. If a seo service promises submissions to enormous numbers of resources, it simply means that the submission database mainly consists of FFA archives and other useless resources.

   Give preference to manual or semiautomatic seo submission; do not rely completely on automatic processes. Submitting sites under human control is generally much more efficient than fully automatic submission. The value of submitting a site to paid directories or publishing a backlink should be considered individually for each directory. In most cases, it does not make much sense, but there may be exceptions.

   Submitting sites to directories does not often result in a dramatic effect on site traffic, but it slightly increases the visibility of your site for search engines. This useful seo option is available to everyone and does not require a lot of time and expense, so do not overlook it when promoting your project.

3.7.2 DMOZ directory
    The DMOZ directory (www.dmoz.org) or the Open Directory Project is the largest directory on the Internet. There are many copies of the main DMOZ site and so, if you submit your site to the DMOZ directory, you will get a valuable link from the directory itself as well as dozens of additional links from related resources. This means that the DMOZ directory is of great value to a seo aware webmaster.

   It is not easy to get your site into the DMOZ directory; there is an element of luck involved. Your site may appear in the directory a few minutes after it has been submitted or it may take months to appear.

   If you submitted your site details correctly and in the appropriate category then it should eventually appear. If it does not appear after a reasonable time then you can try contacting the editor of your category with a question about your request (the DMOZ site gives you such opportunity). Of course, there are no guarantees, but it may help. DMOZ directory submissions are free of charge for all sites, including commercial ones.

   Here are my final recommendations regarding site submissions to DMOZ. Read all site requirements, descriptions, etc. to avoid violating the submission rules. Such a violation will most likely result in a refusal to consider your request. Please remember, presence in the DMOZ directory is desirable, but not obligatory. Do not despair if you fail to get into this directory. It is possible to reach top positions in search results without this directory – many sites do.

3.7.3 Link exchange
   The essence of link exchanges is that you use a special page to publish links to other sites and get similar backlinks from them. Search engines do not like link exchanges because, in many cases, they distort search results and do not provide anything useful to Internet users. However, it is still an effective way to increase link popularity if you observe several simple rules.

   - Exchange links with sites that are related by topic. Exchanging links with unrelated sites is ineffective and unpopular.

   - Before exchanging, make sure that your link will be published on a “good” page. This means that the page must have a reasonable PageRank (3-4 or higher is recommended), it must be available for indexing by search engines, the link must be direct, the total number of links on the page must not exceed 50, and so on.

   - Do not create large link directories on your site. The idea of such a directory seems attractive because it gives you an opportunity to exchange links with many sites on various topics. You will have a topic category for each listed site. However, when trying to optimize your site you are looking for link quality rather than quantity and there are some potential pitfalls. No seo aware webmaster will publish a quality link to you if he receives a worthless link from your directory “link farm” in return. Generally, the PageRank of pages from such directories leaves a lot to be desired. In addition, search engines do not like these directories at all. There have even been cases where sites were banned for using such directories.

   - Use a separate page on the site for link exchanges. It must have a reasonable PageRank and it must be indexed by search engines, etc. Do not publish more than 50 links on one page (otherwise search engines may fail to take some of the links into account). This will help you to find other seo aware partners for link exchanges.

   - Search engines try to track mutual links. That is why you should, if possible, publish backlinks on a domain/site other than the one you are trying to promote. The best variant is when you promote the resource site1.com and publish backlinks on the resource site2.com.

    - Exchange links with caution. Webmasters who are not quite honest will often remove your links from their resources after a while. Check your backlinks from time to time.

3.7.4 Press releases, news feeds, thematic resources
   This section is about site marketing rather than pure seo. There are many information resources and news feeds that publish press releases and news on various topics. Such sites can supply you with direct visitors and also increase your sites popularity. If you do not find it easy to create a press release or a piece of news, hire copywriters – they will help you find or create something newsworthy.

   Look for resources that deal with similar topics to your own site. You may find many Internet projects that not in direct competition with you, but which share the same topic as your site. Try to approach the site owners. It is quite possible that they will be glad to publish information about your project.

   One final tip for obtaining inbound links – try to create slight variations in the inbound link text. If all inbound links to your site have exactly the same link text and there are many of them, the search engines may flag it as a spam attempt and penalize your site.