The structure of a site can impact on the pagerank of individual pages and this article tries to illustrate the concepts behind this and the importance of Link Popularity.

Pagerank was defined in the original Google article as

PR(A) = (1-d) + d(PR(t1)/C(t1) + … + PR(tn)/C(tn))  where d is a dampening factor commonly believed to be 0.85.

So pagerank of page A is 0.15 plus a little bit of the pagerank of each page that links to it ( this share relates to the pagerank of the linking page divided by the number of outbound links on the page).

Thinking of this it can be seen that:-

• adding pages increases the total potential pagerank of a site
• inbound links increase the total pagerank within a site
• pagerank can be distributed around the site by changing the linking structure to funnel it to important pages
• poor linking structures can prevent a site achieving its maximum potential aggregated pagerank as some links are not established
• the allocation of pagerank can leak out of a site when it links outwards (unless using the rel=nofollow tag )

Accordingly it is important to consider the structure of a site and ensure that pagerank is shepherded to the important pages in the site.  In this way they will have higher pagerank and a better ranking in the search engine index.

Some other points to note are

• Pagerank goes from 1 to 10
• the increase is probably logarithmic
• pages with no links to them are classed as orphans by Google and excluded from the pagerank calculations which are iterative

There is an excellent, but complicated, article on this at http://webworkshop.net/pagerank.html