Latent Semantic Indexing for on-page optimizations

How to use LSI keywords to boost your SEO

Back in the day, Google determined relevancy of an article mostly based on keyword density. In other words, the more you use a certain keyword in an article the better your rankings are. This method came to be known as keyword stuffing. As you can imagine, such SEO strategy led to the creation of some pieces of content that were virtually unreadable by a human eye, not to mention they were completely useless.

Of course, given that Google search engine is primarily concerned with finding the best content which can provide valuable information to the end user, keyword stuffing became quite a problem. So, in order to remedy the issue, Google started implementing LSI keywords instead.

What are LSI keywords?

LSI stands for latent semantic indexing. In short, LSI keywords are words that are semantically linked to your main keywords without directly being their synonyms.

Significance of LSI keywords

Today, LSI keywords should be the cornerstone of on-page optimization. These phrases represent all the synonyms as well as related keywords that tend to go together with a certain keyword.

So, how do they work in practice? It’s really simple.

When you write an article, Google finds it very hard to determine which phrase is the most relevant. Given that keyword stuffing is no longer a viable SEO strategy, relevancy of a phrase is now determined based mostly on LSI keywords.

For instance, if you put the word “apple” in a text, without adding any synonyms or semantically related words, Google will perceive it as a random word and will not be able to estimate its value. Being just a machine, it cannot interpret written text like humans. On the other hand, if you use the word several times, surrounding it by numerous LSI keywords, Google will be able to determine the true meaning behind your content.

That’s why understanding how you use LSI to impact the keywords used in your copy has an important function. They allow search engines to properly understand and rank your content in the SERP. Let’s explain this better with an example. When you write the word “apple”, it can mean different things. It can be seen as a software product, a tech company or a fruit. Depending on which LSI keywords you use in your article, Google will be able to classify your article and present it to the correct end user. If you have included words such as “pie”, fruit”, “tree” in your article, it is obvious that you are talking about the fruit. On the other hand, words like “computer” and “OS” will indicate that it is the Apple’s software product that you’re writing about.

The TF-IDF concept

Depending on a topic, Google expects to see certain LSI keywords in a certain number in order to establish which phrase is the most important one. However, have in mind that different phrases have different impact on a text. This is known as term frequency – inverse document frequency (TF-IDF).

Let’s take the word “razor” for example.

A common LSI keyword that goes with this term would be “blade”. In that regard, even if term “blade” is mentioned once or twice in an article, it doesn’t have that much of a value just because Google expects these two words to go together. But, if we add the word “shaving”, it is much easier for Google to establish that the article is about razors that men use to shave themselves.

If the LSI keyword is rarely used (but still has some correlation to the main keyword) it will make your article much more visible to Google. On the other hand, if the LSI keyword is really common, it will have to be repeated numerous times so that Google can establish what the main phrase in the text is.

Improving your TF-IDF score will not give you an SEO boost (unlike keyword stuffing back in the day). Instead, you should see it as a prerequisite that will allow you to be positioned for a particular phrase and as such, a necessary part of your on-page SEO efforts.

How to position your LSI keywords in the text?

Even if you are laymen when it comes to SEO, you probably know that you have to insert your main keyword in the title of your page. When it comes to LSI keywords it is best if you put them within the body of your article. LSI keywords placed in page headers, footers and sidebars are simply not as important as those that are placed within the body of content.

There is another thing that you have to consider when it comes to positioning your latent semantic indexing keywords. You shouldn’t use them randomly in your text. In most cases, they need to be closely connected to each other.

Depending on their placement and distance from the main keyword, Google determines correlation between your main keyword and the LSI keywords that surround it. Ideally, you should place all of them in the same sentence. Naturally, as distance increases, relevancy is reduced. Have in mind that keywords within the title or in the same bullet list are regarded as equally distant from each other.

How to find LSI keywords?       

It is simple. All you have to do is use one of the numerous LSI keyword generators that are available on the internet. Unlike some other SEO tools, LSI keyword generators are usually free. In some cases, you will have to register but that is pretty much that. Keys4up is one of the best tools for this particular purpose. All you have to do is type in your main keyword and generator will give you a list of LSI keywords based on their relevancy. If your site runs on WordPress, you might want to check the SEOPressor plugin which can be really useful.

Some practical tips

Even though LSI keywords are crucial for your on-page SEO, it’s not that hard to find and implement them. In fact, you will most likely add them in your articles yourself, without any previous research, as long as you are writing naturally. When Google first introduced this method, the company wanted people to create normal articles, to write for their visitors instead of search engines.

In that regard, as long as you are trying to provide real value to your readers, you should be able to create a normal article with all these semantic words within it. Furthermore, it is best if you write your article naturally and then polish it by adding a few LSI keywords that you might have missed.

Nikolay Stoyanov is a well-known SEO expert with over 8 years of SEO experience. He's a huge fan of Brian Dean and a proud graduate of his SEO That Works online course. He practices 100% white hat SEO techniques and has a vast experience in keyword research, on-page optimization, SEO auditing and link building. Nikolay enjoys learning new things, making new friendships and improving his skills all the time. You can follow him on Twitter