According to the site, Searchmetrics.com, ¨ Topical relevance is mainly used in conjunction with backlinks. Websites that carry similar content are said to have topical relevance. Backlinks from websites that are topically relevant have more impact on a website´s position in search results than backlinks from sites that are not related. Search engines assume that topically relevant links are used to offer users additional information that could be helpful¨

Although SEO strategies have changed over the years largely owing to Google´s ever-changing search algorithms, the only thing that has remained uniform is the paramount importance of links. However, you should understand that obtaining links from just about anywhere will not help your site at all. You must put more emphasis into getting the right link instead. In current times, a lot of emphasis is given to the relevance of the links.  For instance, the site linking to another site must either provide similar content or additional relevant information and help. If you have these types of links, you will enjoy numerous advantages. However, if the links you possess are irrelevant and if Google categorizes them as spam links, those links will be as useful as vestigial organs in a human body. Luckily for you, all the sites that link to you need not necessarily be pertinent; only the page needs to be relevant.

Performing SEO locally

Although it could certainly help your cause if you acquire relevant links to your site from all over the globe, it could be insignificant when in competition with the local sites that have been optimized masterfully, therefore, preventing you from reaching a high rank in the search engines. Therefore, in such cases, you should aim to get local links to your site regardless of its relevance to your site or the product you offer. This will give credentials to your site and help your reach higher rankings in the local search engine.

Here is one article, although its old, but have good points:

Repurposing Content: 6 Steps to Boost Backlinks & Rankings 5x

Do you frequently make great post on your blog yet you still don’t see the traffic or customers rolling in?
In 2016, creating content is more than just writing niche specific articles on your blog.
Now there are a ton of different types of content and different ways to share these pieces of content. Repurposing Content: 6 Steps to Boost Backlinks & Rankings 5x

The question arises: What will you do to acquire the relevant links that you require?

If you are simply focusing on SEO optimization through links with tropical relevance, you should do everything in your hands to attract the sites that are relevant to your website; you should tempt them into linking to your site. For instance, one of the easiest ways to do so is to write instructional posts. If you are providing solutions on how to change a brake tire, a business website that deals with brake tires will be tempted into linking to your site. Posting pictures of how you accomplished the task on social media platforms can help your site get major publicity too.

Let us be brutally honest here; you might produce wonderful, quality content that boasts of the appropriate length and doesn´t go off on tangents, but the truth is, it can´t promote itself; that´s where you come in! You shouldn´t feel embarrassed to send the content to a relevant site. What do you have to lose? They might not link to your site, and that´s it! Consider the benefits you might potentially get from sending your content to a relevant site; the site could end up sharing the post, in turn, bringing in more traffic to your site, and God forbid, even end up bringing links to your post.

Topical relevancy

When dealing with SEO locally, you should instead direct your focus in a different area. The goal here is to target the local market. However, it isn´t necessary for you to only get links that are relevant to your content and services. The objective here is to get local links to your site regardless of its relevance to your site or the product you offer. This will give credentials to your site and help your reach higher rankings in the local search engine.

So, how do you acquire local backlinks?

When you are attempting to acquire local backlinks, you should focus on grabbing headlines locally. If you generate content that the local station or tabloid would be interested in, you might end up getting the local station or tabloid linking to your site. Another quick-fire method of getting local backlinks is through association with the local charity organizations and businesses.

Therefore, when attempting to boost your links, you should first know whether you want your website to perform well locally or globally. However, by now, you should be well aware of the importance of relevancy; it is not only about acquiring backlinks. If the links you possess are irrelevant and if Google categorizes them as spam links, those links will be as useful as vestigial organs in a human body.