Simplified, to be sure, but more complex beings can saunter over to Matt’s blog and get a more in depth picture – his post was wonderful, and a little distillation will hopefully inspire you to make the visit and be edified…
First off, Matt posts a little disclaimer, which I’ll add here :
Disclaimer: Even when I joined the company in 2000, Google was doing more sophisticated link computation than you would observe from the classic PageRank papers. If you believe that Google stopped innovating in link analysis, that’s a flawed assumption. Although we still refer to it as PageRank, Google’s ability to compute reputation based on links has advanced considerably over the years. I’ll do the rest of my blog post in the framework of “classic PageRank” but bear in mind that it’s not a perfect analogy.
Matt goes on to use some nifty diagrams to detail how PageRank works on a basic level. After that he introduces the concept of PageRank ‘decay’, which posits that 10-15% of PageRank on any given page does not transfer across when PageRank is passed – in other words, a page with a rank of eight might only pass seven along.
The important thing about PageRank especially when it comes to linking and Page Sculpting, is the no-follow attribute. When you nofollow a link, it passes no PageRank and no anchortext (Matt says here that he has seen some isolated incidents of anchortext being passed over the years, but these were anomalies arising from indexing bugs which were fixed.)
Page Sculpting originated with the idea that a page with say 10 PageRank points and 10 outgoing links, 5 of which are nofollowed, will (leaving out the ‘decay factor’) would work something like this:
Originally each link might have passed on 1 point. Since 5 are no-followed, it was hoped the remaining 5 would each pass on 2 points. HOWEVER, Google last year tweaked things so the 5 without the no-follow attribute will still only pass on 1 point each, making ‘Sculpting’ much more difficult.
This was put in place because webmasters were actually making more valuable parts of their site less visible as they attempted to force PageRank to certain pages according to their own advantage – which is not always user friendly. Matt sums it his take on PageRank Sculpting:
I wouldn’t recommend it, because it isn’t the most effective way to utilize your PageRank. In general, I would let PageRank flow freely within your site… I would recommend the first-order things to pay attention to are 1) making great content that will attract links in the first place, and 2) choosing a site architecture that makes your site usable/crawlable for humans and search engines alike.
I pretty much let PageRank flow freely throughout my site, and I’d recommend that you do the same.
Thanks Matt! For the whole story, check out Matt’s superlative Blog.