IA is how you organize all the content of your website or application. It includes navigation, hierarchies and taxonomies.
The information architecture of a website affects all areas of the business from the database engineers to the marketing and sales people to the frontend builders and designers. Customers too are largely encouraged or discouraged from using an application based on how all the content is organized and what they must do in order to accomplish their goals there.
The goal for the product designer is to organize the content of the website or the user flow in an application so that it makes sense to the user.
We organize (some of us better than others) everything in our lives, from the items in the kitchen, to where we store our clothes, the kinds of furniture in each room of our house–even where we park the car. In the digital world we’re cataloging and categorizing too; on Pinterest we name Boards and group items according to styles, types, colors, etc. On Facebook we can make groupings of our friends and organize our posts.
When we look for a book on Amazon we don’t look in the same place as when we’re buying tea or a new pair of shoes.
Imagine trying to find a single document in a giant filing cabinet filled with documents that are not organized alphabetically or in any other understandable hierarchical system.
Or imagine looking for a particular dish in a kitchen where cupboards and drawers had no organizing principle.
That’s what it feels like for users who arrive at websites that look like this:
Just being visually tidy in the UI design is not enough. Here is Amazon’s home page, which is neatly designed but still a chaos of disorganization.
Without some kind of hierarchical organization, confronted with a website like these make our eyes glaze over and our fingers twitch to click is right out of there as fast as we can. If your goal is to keep users on your website (which it always is) then that’s the last impression you want to make on users.