Why we need site arcitecture?
Every site built of many layers, and a good
site architecture will enable the users and search engines find their way around the site much easier.
It’s about getting the most relevant content in front of users and reducing the number of times they have to click in your site to find it. The same applies to search engines, by reducing the number of layers in your site architecture; you can potentialy gain better indexation metrics such as the number of pages generating search engine traffic and the number of pages in a search engine index.
The principle of reducing the number of clicks between your homepage and your deepest layer of content is as important today as it ever was due to the many different criteria indexing is done.
If a site is complex and contain 6 layers from the home page to the deepest page content, most likely the 6th. layer will not get "any attention" from search engines or users.
Most SEOs argue that pages buried very deeply in the architecture might not receive enough link juice to be visible in search engine rankings. If we can flatten the site to a 3 layer instead deep instead of 6 then we promoting content “up” the architecture, and you can improve its overall rank. This process is called “flattening”.
The diagram below illustrates how a good site architecture should look like:

Here, we've increased the number of links on each page and reduced the number of clicks to reach the deepest level of content, effectively flattening the
site architecture.
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