What is Google PageRank?

Understanding PageRank is fairly straightforward, it is the matter of calculating a pages importance based on reputation - or the number of reputable sources have linked to that page from elsewhere on the internet.

PageRank is proprietary to Google, however, all the major search engines incorporate similar ‘page importance’ calculations in their algorithms.

A Few Important Points About PageRank:

• PR is assigned to individual pages, not to a site
• PR is any value between 0-10, it is not scalar as it seems in the little green bar, this is just an approximation of the actual value
• PR does not increase uniformly based simply on the number of pages that link to your page
• PR operates on a logarithmic scale, meaning the jump from 6 to 7 is far harder to achieve than that jump from 5 to 6

The PageRank Algorithm:

In its simplest form, the PageRank for a page is inherited from pages that link to it…

  pr(A) = pr(B) / t(B) + pr(C) / t(C) ... pr(N) / t(N)

Where

• pr = PageRank of the page
• t = outgoing links from the page

Therefore, pr of A is found by calculating the pr of page B divided by the number of outgoing links from B and the pr of page C divided by the number of outgoing links from C.

Easy huh? This process extends as you would naturally imagine.

For Example:

In this basic example consider that all pages start with a PageRank of 1.

To calculate the PageRank of A:

• pr(a) = pr(b)/t(b) + pr(c)/t(c)
• pr(a) = 1/2 + 1/2
• pr(a) = 1

As you can guess pages B and C will be the same. Therefore, in the linking structure below no pages benefit.

However, if we alter the example slightly….

Here you can see that page A is missing one of the previous inbound links. Therefore the new calculations of the PageRank system are as follows…

• pr(a) = 1/2 = .5
• pr(b) = 1/2 + 1/2 = 1
• pr(c) = 1 + 1/2 = 1.5

You can clearly see how the PageRank has been adjusted and redistributed around the system. It is important to note that PageRank is calculated as a closed system, the increase of pr for page C is a direct result of decreasing the pr for page A.

It is also important to note that the system iterates many, many times inorder to get accurate figures, this is necessary because each pages rank is based on the rank of other pages, so it must be calculated over and over in order to increase accuracy.

*this is a VERY basic example of how PageRank is calculated

Profile:  Frank has been programming for the web using PHP, Javascript and numerous libraries and frameworks for the past 5 years. More articles.