Latent Semantic Indexing, or LSI, refers to a specific type of keywords that search engines use to refine their results. This particular variety of keywords is used by search engines like Google to display contextually relevant content to the searchers.
So what exactly are LSI keywords and how do they work? More importantly, why should they matter to your SEO efforts? Below, we will take a deep dive into LSI and examine how you can use it to improve your search engine rankings.
First, let’s start by better defining latent semantic indexing. It is a technique in natural language processing, in particular, distributional semantics, of analyzing relationships between a set of documents and the terms they contain by producing a set of concepts related to the documents and terms. LSA assumes that words that are close in meaning will occur in similar pieces of text (the distributional hypothesis). A matrix containing word counts per paragraph (rows represent unique words and columns represent each paragraph) is constructed from a large piece of text and a mathematical technique called singular value decomposition (SVD) is used to reduce the number of rows while preserving the similarity structure among columns. Words are then compared by taking the cosine of the angle between the two vectors (or the dot product between the normalizations of the two vectors) formed by any two rows. Values close to 1 represent very similar words while values close to 0 represent very dissimilar words.
Sounds simple enough, right? Ok, so for non-mathematicians, latent semantic indexing basically means that Google and other search engines are not just looking for a keyword but other keywords that should surround the primary keyword based on the topic.
Suppose you are searching for the term ‘Aladdin.’ Now, Google wants to understand your intent behind the query and then display relevant results. The better Google understands the intent, the more accurate will be the results displayed in response to the query. But when you use a keyword as generic as ‘Aladdin’, this creates a problem for Google. Why? Because Aladdin could mean a whole host of things. It could refer to the legendary character of Aladdin, the story of Aladdin, the video game Aladdin or one of the many movies and cartoons based around the character.
So how does Google know which of these you are looking for? This is where LSI keywords come in. By looking for contextually relevant LSI keywords, Google is better able to understand what you are looking for. In the case of ‘Aladdin’, relevant LSI keywords can be ‘movie’, ‘story’, ‘character’, ‘cartoon’ and so on. These keywords further refine the original keyword and make it more obvious to Google what you mean.
The ultimate aim of Google and other search engines is to deliver relevant results to searchers. LSI keywords are a key part of how search engines do this because they help describe intent.
When you introduce LSI keywords, you gain an immediate advantage over other sites. By adding context to your primary keyword through the use of LSI keywords, you make it easier for Google to understand the overall theme of the page. In return, Google shows your content higher and more frequently for relevant queries.
In addition, LSI keywords also make it easier for the right audience to reach your content. When searchers use an LSI keyword alongside the primary keyword, they know exactly what they are looking for. When you use LSI keywords, you are able to target this audience and improve user engagement.
For a search term like ‘Aladdin’, a search will most likely be adding more to it like ‘Aladdin movies’ or ‘Aladdin movie trailer’ to help the search engine find its results so that is an easy to understand example. Where it gets more tricky is when your keywords help provide the context. Imagine I am searching for the term ‘implants’ in Google. Implants could be associated with a number of things like breast implants or dental implants. If I am optimizing a website for a dentist, I want to make sure that someone searching for ‘tooth implants’ or ‘implant dentist’ is directed to my page but I don’t care about ‘breast implants’. To do that, I can use LSI keywords to add context to my page. I could look at variations of these terms like ‘types of dental implants’, ‘dental implant procedure’, and ‘ dental implant problems’ on my page to not only cover a range of keywords that a user might search for, but will also help my page be an authoritative resource for the general topic of dental implants. In this case, even if someone is not searching for my LSI keywords they still provide value to the context of the page and demonstrate that my page thoroughly covers the topic the user is searching for!
If you want to optimize your SEO strategy with LSI keywords, it is important to find the right complimentary keywords. The right LSI keywords are both related to your content and contextually relevant to the search.
Here are some great places to look for the right LSI keywords:
Suppose you are looking for the LSI keywords related to ‘cars.’ The quickest and easiest way to do this is by searching for ‘cars’ in Google. Now go through the search results displayed for this primary keyword. Scroll to the bottom of the page and you will see the ‘Search related to cars’ section, as shown in the image below:
The graphic shows closely related keywords to ‘cars’ include ‘movie’, ‘film’, ‘used’, ‘sale’ and so on. You can also go back to the search results and see the ‘cars’ keyword highlighted in bold. Look for the words used immediately next to this primary keyword. LSI keywords like ‘reviews’, ‘magazine’, ‘shopping’, ‘for sale’ and ‘prices’ are used immediately next to the primary keyword. These can serve as very effective LSI keywords for your content.
Another excellent tool to look up LSI keywords is the Google Keyword Research Tool. To use this tool, simply punch in any search query or keyword and you will be presented with a long list of results. You can see the LSI keywords used in conjunction with the primary keyword. You will also see the monthly volume and other metrics related to these keywords in order to shortlist the ones that are most suitable for you.
The LSI Graph tool is specifically aimed at providing you with relevant LSI keywords. To find relevant LSI keywords, simply put any query into the tool and hit ‘Generate.’ You will receive a response with a long list of results, as shown below
LSI keywords are a vital part of a successful SEO strategy. However, they are only a part of the equation. Do not overuse them or use them out of context but instead use them to make your page a better resource for visitors. When you’re choosing keywords, choose only the ones that are genuinely relevant to the content you are offering your target audience. Use them where relevant and without breaking the flow of your content.
It is a good idea to incorporate LSI keywords into your regular keyword research effort. This will make sure that you are also able to give due attention to other aspects of good SEO, such as quality content and relevant backlinks.
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