
Even though theme density is not a well known term in search engine optimization, many will come to know this as SEO evolves. The root of this SEO model is based on semantic relationships, co-occurrence of synonyms, polynyms and thematic modifiers.
The end result, multiple top 5 and top 10 rankings for broad match and exact match keywords and key phrases (which all add up over time). This strategy is based on the premise of using multiple pages within a website to concentrate a particular ranking factor and then transfer that ranking factor to a singular or multiple target pages.
Wikipedia is known best for this tactic, so, questioning the effectiveness of the method would be a moot point. Each keyword represents a virtual theme for Wikipedia, with its own H1, sub folder in a sub domain and a high concentration of internal and external links.
The prerequisite however is that this tactic requires a larger website, preferably over 1,000 pages in order to harness its full potential. The benefit occurs over time as each page gets indexed and adds yet another layer to the process of SERP domination.
Say for example you wanted to rank for a specific range of keywords like business to business internet marketing for example. Since this key phrase has polynyms as well as a number of interesting shingles (word groups). You can approach it from many angles when building internal and external links. Shingles such as b2b marketing, business to business online marketing, Internet business, Internet marketing and others exist within this context.,
By concentrating content, several articles, blog posts or pages within your website to cross reference a specific pinnacle, you can effectively stem or blossom keywords for each page and the entire website respectively. First, you may witness a page ranking for more than one keyword, then stemming into long tail keywords (keywords with more than 3 words) then sometime peculiar happens over time.
Semantic stemming is when a page starts to rank for competitive combination of keywords within the title, description or body text. The next stage is when the page starts ranking for sparsely related queries and encroaches on other searches as a relevant result with a mere mention in a title, or somewhere on the page. A website with a high concentration of inbound links, trust rank or authority can easily push a search result right into the top 10 from a title tag alone. Other less fortunate sites will have to work much harder to cross the tipping point.
Although each keywords top 10 threshold is a moving target, the website with the least resistance to the dominant ranking factor required for that “exact match shingle” a.k.a. keyword or “key phrase” will have to tap-out when someone nails the semantic threshold for on page factors, has sufficient link flow from within the website and is augmented by a tinge of trust rank.