Internal Linking to Promote Keyword Cluster explained the math of how strength passes internally between pages of a website and how it can be influenced with a focused and planned internal linking structure. The limitation of this approach is that it assumes that all internal links are created equal. This isnt the case.

Several factors influence the weight and relative importance of an internal link. For example the format of that link, its position on the page, its position relative to other links, etc. While the specific way that the engines weigh individual links is not known (and would likely change even if it was), there are principles you can be apply to understand how the weight is being carried through your site past simple mathematics.

The simplest (and arguably most effective) first step is to think like a visitor. In the desire for search engines to provide as relevant a result as possible, they work hard to emulate as best they can a visitor experience.

While the fine folks at Google (and Bing of course) can't visit every site on the web, they can create automated systems that do an excellent job at understanding how the web works, how elements are positioned on a page, and what those elements look and behave like. From this they can gather an understanding of how important a link is.

Let's look at the following basic diagram of a simple website (the dotted line indicates where the fold line is, everything above it is visible to the average user on first visiting the site):

The rule of thumb you can follow is this: the more visible the link is, the higher the weight it will pass. Let's look at each of the main link elements and grade them on a scale of 1 to 10:

I list the sidebar links first as I tend to use them as my baseline. Sidebars are often the spot for links you want people to be able to find easily enough but not important enough to make it to your main navigation. They are positioned above the fold, however there are usually many of them in a list, thus reducing their visibility. When I'm thinking about my weighting of links, I usually use the sidebar links as the baseline at 5 and grade the rest up-or-down from there.

This is the single most visible link area on a page. The majority of websites use the logo as a link to the homepage. The weight of this link will be high as Google knows that this link is extremely visible and highly clickable. As far as a link zone is concerned, the header is the 10 as far as potential weight passing is concerned.

These links are highly visible and engines know that these links tend to point to the key pages on a website. This is where you as a visitor look to find product or contact information, and the engines know that. Pages linked to in this area will be given a high relative weight. This zone is given a 9 out of 10 for weighting.

Continue reading here:
Anatomy of an Internal Link