Contrary to popular belief, Google's PageRank algorithm doesn't only apply to external (i.e., outgoing and incoming) links -- it can also be used as a self-contained analysis tool to determine health, strengths, and weaknesses of your website's on-site links.
Of course, this has nothing to do whatever with the Toolbar PageRank (TBPR) Google has been using as a brilliant tool of social engineering for years, eminently safeguarded by plausible deniability all along. According to Google, it is, after all, intended "for entertainment purposes only."
So why is this important? Consider: out of the 150˜190 or so individual factors governing a website's ranking (who outside of Google can ever know for sure how many they are exactly?), there's only a handful you yourself have full control over.
First comes content, obviously: it's the one thing the search engines can't and won't create for you. Then there are other on-site elements, such as meta tags, title tags, the canonicals specification, page architecture, etc. Last, but not least, there's your on-site linking structure.
In a nutshell, here's what you may get if you fail to optimize your on-site links:
- Non-indexed pages
- Pages dropped into what used to be called Google's "Supplemental Results Hell"
- Pages relegated to Google's "Omitted Results" filter
- Orphaned pages
- Broken links impeding rankings and accessibility
Websites that have grown "organically" in the course of the years, with several generations of webmasters and system administrators having tended to them (not to mention management, sales departments and creatives -- think redesign!) are inevitably bound to encounter problems with their on-site linking structures sooner or later. Remember good old techie terms like "link rot"?
Nor is this "organic" (i.e., human component) the only culprit involved. Content management systems (CMS), which drive a huge chunk, if not the overwhelming majority of large corporate sites, are another prime issue generator.
Many major CMS providers have latched onto the fact that "SEO" is all the craze now, so they take great pains to voice their claim that their systems have "full SEO features" implemented. Generally, this is, however, limited to including customizable (i.e., not entirely templated) meta tags, title tags, and keyword rich page or file names. From a professional SEO's point of view, this still leaves a tremendous lot to be desired. And, in any case, an optimized on-site linking architecture addressing a given site in its entirety doesn't seem to be part of their SEO efforts anyway.
What's worse, many sub-optimally organized sites aren't even their respective CMS's fault. Content management systems are, after all, pretty complex tools, and if the staff charged with implementing and configuring them aren't 100 percent sure of what they're doing, especially as regards state-of-the-art SEO requirements, it doesn't take an Einstein to figure out what you'll get in the end, and as a rule it's anything but pretty.
Finally, there's another important factor that may prevent your on-site linking architecture from being optimized the way it should be from a pure SEO perspective: your real life promotion environment. Regardless of whether you're trying to push sales online, solicit leads, offer customer support or establish and fortify your brand -- you'll have your own, perfectly legitimate views of how to present yourself to your clients.
This will typically encompass specific, indispensable elements of design and corporate identity factors ranging from logos to icons and color schemes. And, yes, you may actually prefer a specific, non-standard type of site architecture for the very same reason as well.
(For example, you might want to focus on pushing your products overview or your customer survey pages rather than your mission statement or your news section. Some sites want their visitors to engage in some Flash based interactive features, such as an online game or a quiz, while others may prefer to point potential buyers to their global resellers network, etc.)
More often than not, this will mandate some kind of trade off between what would be the optimal linking structure from a purely SEO driven point of view, and whatever real world requirements need addressed.
Leverage Google's Published PageRank Algorithm
In any case, you should always be aware of what you're doing -- and every single on-site link ought to have its own objectified rationale backing it up. In our experience of some five years investigating this matter, analyzing large corporate (usually CMS powered) websites, and optimizing their on-site link architecture, we've found that leveraging Google's published PageRank algorithm (in contrast to whatever modified version of it they may be deploying as part of their top secret internal ranking algorithm) offers us excellent, unbiased metrics to determine a given site's linking fortes and soft spots.
Nor can this be ignored with impunity: arguably the trickiest aspect of the matter is the fact that you may actually be losing search engine rankings, traffic, and sales due to a non-optimal on-site linking structure -- without even being aware of the fact!