Jakob Nielsen discusses structure and navigation in IA ...
"Structure and navigation must support each other and integrate with search and across subsites. Complexity, inconsistency, hidden options, and clumsy UI mechanics prevent users from finding what they need.
Bad information architecture causes the majority of outright user failures and isn't improving at the rate of other Web usability issues. To determine why, I've identified 10 long-term sore thumbs that together cost websites billions of dollars each year.
I divided the following list of worst IA mistakes into two parts, which corresponds to how we partition the materials across our 2-day IA course: structure on Day 1 and navigation on Day 2. Of course, you need to get both right, but they're essentially two different design levels: The invisible way the site is structured and the visible way users understand and manage that structure.
1. No Structure
The most notable structural problem is when designers treat a site like one big swamp with no organizing principle for individual items. Yes, users can fish the swamp using search or by following links from current promotions or outside sites. But whatever they dredge up is it. No opportunities for understanding the site's other offerings or locating related items.
This sin is common on news sites and catalog-based e-commerce sites, where each item (articles and products, respectively) is treated as a stand-alone unit without connections to related items. No wonder users leave those sites so quickly.
2. Search and Structure Not Integrated
We've long known that users often exhibit search-dominant behaviors. This doesn't mean that search is all they need, however. Arriving on a page from a search is like parachuting into a city. Hopefully, if you want to go to Paris, you'll land there rather than in Amsterdam, but in any case, you're unlikely to land on the doorstep of your favorite restaurant. To get there, you'll need to walk or take a cab. Similarly, users often need to navigate the neighborhood around their search destination.
Of course, local navigation works only if the site has a structure to define its neighborhoods (see mistake #1). But the design must also expose local options to users. Even better if it indicates how relevant the neighboring options are to the user's current query.
SERP (search engine results page) usability increases when each search hit exposes its location within the site structure. External search engines like Google can't always do this because they don't know the site's structure or which navigational dimensions are most relevant to common site tasks. But you do know your site's structure and should therefore include the info on your own SERPs.
Sadly, search and navigation fail to support each other on many sites. This problem is exacerbated by another common mistake: navigation designs that don't indicate the user's current location. That is, after users click a search result, they can't determine where they are in the site — as when you're searching for pants and click on a pair, but then have no way to see more pants.
3. Missing Category Landing Pages
We recommend that sites have a series of categories that each link to their own landing page that gives users a section overview. Sometimes, sites forego the overview page and simply offer links directly to individual pages within a section. This might reduce the number of site pages, but when no page is clearly identified as a sub-topic page, users can misunderstand the site's scope and miss important details, products, and services.
Category pages also help SEO because they're the most prominent landing place when people search for a type of product, service, or information. They're also a way to overcome mistake #2 because they help users bump up a level or two in the site structure if search takes them to an overly detailed leaf node. (Breadcrumbs facilitate users' ability to easily move up the levels.)
4. Extreme Polyhierarchy
Compared to the physical world, one of the online world's benefits is that items can live in multiple locations. Because websites can classify products and other content along multiple dimensions, they help users navigate locally to related items and provide faceted winnowing of a large product space into manageable shortlists that can satisfy the user's main requirements.
This is all good, but polyhierarchy can easily become a crutch. Rather than spend time upfront to develop several intuitive and logical top-level categories, teams rush through this important process, creating numerous weak categories and listing products multiple times within them. The usability impact? Users spend too much time agonizing over top-level categories and then get confused when they see items showing up in multiple places ("are these the same thing?").
With too many classification options and too many structured dimensions, users are forced to think harder to move forward. The profusion of options also makes people question the information scent. This lack of confidence early in the site experience extends throughout their visit and can negatively impact the end result (by thwarting a purchase, for example).
Poorly Integrated with Main Site
Abandoned microsites litter the Web as the detritus of old marketing campaigns. A dedicated microsite might have been a good idea back when you launched a new product, but by the next year it's undermining your online strategy and diluting your online presence.
Web design is design for the ages. Think about how anything you do will feel in 5 years.
It's typically best to forego independent microsites and place new information on subsites within the main site. But you still need to integrate these subsites within the overall site structure.
For example, on both microsites and subsites, we often see product-specific pages that fail to link to information about the company or organization behind the offering. Further, many sites poorly represent their subsites in the main site search — which often ignores microsites altogether." (Continued via Jakob Nielsen's Alertbox) [Usability Resources]