Information architecture can be defined as the structural design of information. It combines organisation, labelling, search and navigation systems to present that information in a logical way.
The first question to address on your website is who the information is intended for, and however simple that question may appear there are two main competing interests each championed by its own discipline…
…you want to offer human visitors what they want and in a way that is logical for them to use but you also want to appeal to search engine algorithms to get visitors to find your site in the first place. So when shaping information there is a continual need to balance the requirements of Google’s computers and the desires of the human you want to sell to. (Additionally you want to present your company in the way that is logical to you and how you want others to see it, but that’s a different battle.)
The purpose of SEO is to attract search engine computers to the page.
The SEO perspective aims to improve the crawlability and indexation of the page so that the site appears high on the list of search results generated by Google computers. It uses techniques (such as the nofollow attribute, robots exclusion protocol, cloaking, etc.) to sculpt the page rank, for example by repeating and highlighting specific keyword phrases on a particular page. SEO communicates with computers.
In contrast usability experts seek to provide information in the most user-friencly format to the humans who arrive on the page.
If we take the example of keywords, the user seeks clarity and has no need to see the same phrase repeated ad nauseum for no reason as happens in the extreme SEO case of ‘keyword stuffing’, such as:
Are you looking for cheap tennis shoes? If you’re looking for cheap tennis shoes, you’ve come to the right place. Our cheap tennis shoes store is the best place to buy your new cheap tennis shoes. Please check out our selection of cheap tennis shoes from our cheap tennis shoes selection.
Clearly such contrived text will discourage the visitor from staying on the site regardless of how stratospheric a ranking was achieved on the search engine results page. Search engines do strive to ignore obvious manipulation in favour of listing genuinely useful pages but the example of keyword stuffing illustrates the following point: