It takes a wizard to understand Google's calculations on ranking a site. To have a full understanding one must track all the changes the Google ranking formula underwent since its inception.

One can say that PageRank is the fundamental unit of Google algorithm on which Google bases its calculations. No matter what the SEO professionals think with respect to the importance of pagerank in Google algorithm, there is little room for doubt that Google considers it to be important. In Google's history itself one can track varied emphasis placed by Google on pagerank.

Pagerank as it stands now as a monster, started as a simple formula which over time has gained its momentum and complexity.

Pagerank is calculated not merely based on the number of links on a page. SEO technicians today have come to the understanding that it is more of a complex process that involves many more factors.

Some of the factors that have been included are sending and receiving page themes and sending and receiving of page topics which as lead to the evolution of a new SEO field, Topic Sensitive PageRank (TSPR)

Thus, SEO experts are constantly on the run to update themselves and to consider many more new factors than ever before. Therefore, there is a need to explore into all possible factors used in that new calculation, including Topic Sensitive Page Rank. Such an understanding will help you to improve the page rank for all your web pages.

PageRank was originally a voting system which counted every link to a page as a vote for that page. Higher the value of votes on a page, greater the significance of that page in the eyes of Google. When a site is assessed important, votes from those sites to other pages will be given more value by Google. Thus adding quality incoming links to your pages will add value to your page rank. However every inbound link adds something to your pagerank irrespective of its own level. Thus it is evident that pagerank flows from one page to the other. Nevertheless, this simple concept is no more this simple it has undergone severe alteration with time.

As it stands now, not every incoming link that offers the same inflow of points. For instance it will consume a lot of PR2 incoming links to enhance your page to PR5, where as it will take only one PR6 link to produce the same effect.

The following is the Google's original PR calculation formula:

PR(A) = (1-d) + d(PR(t1)/C(t1) + ... + PR(tn)/C(tn))

Though no one is not sure whether Google still uses this formula, it is probable that the new Google PR formula is very similar.

Just to understand the formula:

PR(A) is the PageRank of the page

d is damping factor considered to be about 0.85

t1 is the PR of the incoming link page

C is the number of outgoing links from each page.

It can be noticed that the PR flow of a page is equally distributed through all the links on the page. If a page receives an exclusive link, then the page that receives the link will get the entire flow, where as if it is not an exclusive link to that page and if there are 5 links on the page, then the PR flow will be divided by so many times, lessened by the damping value .85.

Thus, this is how the formula will look:

PR(A) = .15 + .85 * the PR share of every incoming link page.

Greater the number of links from higher PR pages better the results. Secondly, fewer the outgoing links from the sending page, better the results on the receiving page.

Theoretically, a page gains greater PR from an exclusive PR4 link than from a PR8 link which flows out to hundred different pages. Though not all incoming links have the same value, the bottom line is to gain as many incoming links as possible.

The original Google pagerank formula can just serve as a guideline to calculate the potential pagerank from a donor page, but cannot guarantee anything in its entirety.

Google's constant changing algorithm is the basic reason for this uncertainty and hence can only be speculations.

The pagerank of any given webpage had its own value as it was of little concern on the relevant relationship between the sending and recipient pages. But now, things have changed, Google's changing policies have apparently placed extra dampers which along with Topic Sensitive Pagerank dynamics does not allow the full transfer of pagerank with the incoming link.

An obvious repercussion is that not all incoming links have equal levels of pagerank transfer. You can secure good pagerank from a page that has content relevancy with your website. Page sharing with similar or complementary sites will secure higher pagerank inflow. This adds to the efficiency of the search engine search results which is any search engine's ultimate goal and Google is no exception.

It has to be admitted that pagerank may not be the most important aspect of Google algorithm, it does carry certain weight. Google concentrates more on the incoming links, anchor text and content relevancy after the infamous "Florida Update".

Accuracy is an utopian dream of every online system. Topic-Sensitive PageRank is one such attempt to make the system of PageRank potentially more accurate. In the past it has been that a single page ranking was assigned and now with the TSPR system, multi rankings are created for each particular topic.

Here the topics that are used for the tabulations would represent the theme of each web page. This enables the creation a number of pageranks for each document making the PR theme sensitive using a number of pre-calculated topic based vectors.

Thus, there is a heavy shift in the Google algorithm from the incoming links to the Topic Sensitive Pagerank with content relevancy. Pages with little content relevance will gain little importance in Google's calculations.

In the Topic Sensitive Pagerank system, content relevant pages though with few incoming links will be given more importance while a page with lot of incoming links but with no content relevancy will be of little importance in the eyes of Google.

Like Google PageRank system, the Topic-Sensitive PageRank system can also be pre-computed, to save time in the search query processing. With the TPSR each page will be marked for multiple topics, resulting in multiple PR numbers depending on the total number of topics used. All these added to the old Google PR formula makes the present Google algorithm ever more complicated.

The following example will help you to understand Google's pagerank formula to a certain extent. Please note that all the figures that are used are theoretical.

Let us assume that a sending page has no topic relevancy with the receiving page and has several outgoing links, such a page will bring pagerank of 1 point, which would be the minimum possible value of one point.

Second instance would be a sending page with no content relevancy with the receiving page but with few outgoing links might bring in two points.

As a third situation, a sending page with content relevancy, but with many outgoing links might bring in three points of pagerank.

Whereas a page with close topic relevancy with the receiving page and with only few outgoing links might bring in 4 points of pagerank.

Thus it is evident from the example, that topic relevancy is crucial to the new pagerank formula and the number of outgoing links from the page too is equally important.

In conclusion, though no one can deny that the Google algorithm has changed, no one knows the formula that is currently employed. All that can be said about the new formula is that it is Topic-Sensitive Pagerank based, pages with similar content will help another web page more than pages with no topic relevancy.

Google is constantly refining its formula fine-tuning their calculations to keep itself a viable part of the overall Google algorithm. We can still expect for more changes and refinement from Google which will be geared towards being more topic sensitive to receiving page.

Bearing in mind the above points while adding links will help you achieve best out of the new Google algorithm.