If you'd like to know the differences between a flat versus deep architecture in regards to SEO, then this excerpt from The Art of SEO will interest you.
One very strict rule for search friendliness is the creation of flat site architecture. Flat sites require a minimal number of clicks to access any given page, whereas deep sites create long paths of links required to access detailed content. For nearly every site with fewer than 10,000 pages, all content should be accessible through a maximum of three clicks from the home page and/or sitemap page. At 100 links per page, even sites with millions of pages can have every page accessible in five to six clicks if proper link and navigation structures are employed. If a site is not built to be flat, it can take too many clicks to reach the desired content, as shown in Figure 6.9. In contrast, a flat site (see Figure 6.10) allows users and search engines to reach most content in just a few clicks.
Flat sites aren’t just easier for search engines to crawl; they are also simpler for users, as they limit the number of page visits the user requires to reach his destination. This reduces the abandonment rate and encourages repeat visits.
When creating flat sites, be aware that the engines are known to limit the number of links they crawl from a given page. Representatives from several of the major engines have said that more than 100 individual links from a single page might not be followed unless that page is of particular importance (i.e., many external sites link to it).
Following this guideline means limiting links on category pages to 100 or fewer, meaning that with the three-clicks-to-any-page rule, 10,000 pages is the maximum number possible (unless the home page is also used as a Sitemap-style link guide, which can increase the max, technically, to 1 million).
The 100-links-per-page issue relates directly to another rule for site architects: avoid pagination wherever possible. Pagination, the practice of creating a list of elements on pages separated solely by numbers (e.g., some e-commerce sites use pagination for product catalogs that have more products than they wish to show on a single page), is problematic for many reasons. First, pagination provides virtually no topical relevance. Second, content that moves into different pagination can create duplicate content issues. Last, pagination can create spider traps and hundreds or thousands of extraneous, low-quality pages that can be detrimental to search visibility. Figure 6.11 shows how pagination structures do not benefit search engines.
So, make sure you implement flat structures and stay within sensible guidelines for the number of links per page, while retaining a contextually rich link structure. This is not always as easy as it sounds. Accomplishing this may require quite a bit of thought and planning to build a contextually rich structure on some sites. Consider a site with 10,000 different men’s running shoes. Defining an optimal structure for that site could be a very large effort, but that effort will pay serious dividends in return.
Learn more about this topic from The Art of SEO.
Four acknowledged experts in search engine optimization share guidelines and innovative techniques that will help you plan and execute a comprehensive SEO strategy. This second edition brings you up to date on recent changes in search engine behavior—such as new ranking methods involving user engagement and social media—with an array of effective tactics, from basic to advanced.