Search Engine Optimization (SEO)

SEO involves ensuring that a given site appears on a search engine’s results page when a web user enters a search term. The term SEO is also used for: « Search Engine Optimisation ». The notion of optimisation is central – the aim of SEO is to optimise a site so that it is perceived in the best possible light by search engines such as Google.

SEO deals with so-called ‘natural’ links, as opposed to ‘paid’ links suggested by Google AdWords on results pages.

95% of web users in France
use Google
SERP search engine results
mot-clé the search term entered by web users and
for which sites aim to rank highly

SEO – How does it work ?

How a search engine works

A search engine is an application that extracts sites from the web that meet the terms of a search performed by a user, which are then listed on the results page. The key element to remember about how search engines work is that they rank their results – they order the sites they present using quality criteria. This means that search engines see the first item in the list as the most relevant page that provides the best response to the user’s search.
Each search engine has an index in which it looks for sites to rank. It uses bots (called ‘crawlers’) to look through websites and save them in the index. These crawlers give the search engine a constantly updated database, to which new sites are added and previously visited sites are updated.
In summary, a search engine works via four stages:
  • Crawling The search engine’s bots
    crawl the web
  • SEO The search engine saves
    these sites in its index
  • Ranking The search engine ranks these
    sites based on their quality
  • Results Search engines display results in order of relevance to the query.

Google is currently the most powerful search engine in the world, and is also the most popular search engine in France.
As such, most SEO work is directed at Google.

What is SEO? Search engines rank sites on their results pages. To be ranked highly, they need to be seen as the most relevant result. The aim of all SEO work is therefore to get search engines to ‘understand’ that a given site is the most relevant.

Ranking criteria Google uses criteria to judge a website’s quality. To sum up, they fall under four main categories:


Popularity (linking) is still the main criteria Google uses to assess a site’s relevance. It is measured by the number of links pointing to a site. From the search engine’s viewpoint, the more links a site receives, the more web users are using it as a point of reference, meaning that it is relevant. In Google’s view, popularity is the result of a high-quality site, as if it was low-quality, web users would choose not to share it.

An SEO strategy always includes the idea of popularity. Measures to improve a site’s SEO include analysing backlinks to ensure that the majority come from sites that are already viewed positively by Google to maximise their effect. The search engine will then be more likely to judge a site positively if other authoritative sites publish links to it.

However, the concept of popularity has changed significantly in recent years, and Google has improved the algorithms (Penguin) it uses to measure this criterion. It now plays a more balanced role in SEO. Google also looks to other criteria and the quantity of links alone is no longer sufficient to be seen positively.


The second of Google’s main criteria is content quality. To be seen as relevant, a site should feature content that provides a high-quality response to web users’ queries. Google determines the quality of content by comparing it to reference sites with a similar theme that are already at the top of its rankings.

Content is at the heart of SEO. Optimising your content is central to giving a positive impression to search engines. Your content needs to contain keywords and belong to a semantic sphere to allow Google to properly understand the meaning, and it must also make clear use of tags (title tags, h1 and h2 tags, etc.), which make the bot crawling stage more efficient.

« Quality first » is the new approach to producing content. Thanks to its Panda algorithm and better understanding of more complex queries due to RankBrain, Google can now check content quality more accurately, which is why this criterion has gained ground over quantity.


In order to work properly, Google requires unbelievable amounts of resources. The better the quality of results the search engine wants to provide, the greater the demand on resources will be as crawlers and algorithms have more work to do.

Indexing a website also involves optimising its performance. This means working on its structure in order to limit the number of layers, as this allows Google’s crawlers to gain access to the site’s pages as quickly as possible. Other areas of focus include reducing page load time to a minimum and ensuring that the code complies with international standards.

A site with better performance will simplify Google’s work, as it requires fewer resources. The better optimised the site is, the more pages the search engine can crawl in a single pass, meaning it will be crawled regularly. Any changes made will be taken into account by Google more quickly, and the impacts in terms of SERP ranking will also be more immediate.

User experience (UX)

Google strives to ensure that its users get the best experience. When users perform a search, they should be presented with relevant sites so they are given the correct answer in the best possible way.

Out of all of the ranking criteria, user experience has probably undergone the biggest increase in importance in recent years. Working on search engine optimization without considering its impact on users has now become unthinkable. For this reason, a ranking strategy must include UX recommendations.

One of the most meaningful examples of the importance of user experience is sites’ mobile-friendliness. Google now views sites that are not ‘responsive’ less positively, despite the fact that they might be very popular and have high-quality content.

The role of an SEO agency

An SEO agency helps brands with their online visibility strategy. Brands may contact agencies when creating their site so it can be optimised at a very early stage, following a drop in rankings due to a penalty or to inappropriate actions, or throughout a site’s lifetime to ensure it is constantly seen in a good light by Google. At Primelis, we firmly believe that SEO is a priority marketing driver for brands that want to establish their online presence for good. However, it cannot be dealt with in isolation from other aspects – as the leading source of traffic and a marker of credibility in web users’ eyes, SEO must play a central role in website development.

Indexing a site on Google requires a 360° vision that includes a variety of different aspects: writing content, technical optimisation, analysis, monitoring, UX studies, and more. Even within SEO, the divides between specialisations are becoming more and more marked. The advantage an agency such as Primelis provides is its ability to combine these various areas of expertise, giving brands a comprehensive SEO experience through its team of consultants who keep in constant communication and, where required, use proprietary tools (such as our semantic tool Occurus).

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