Trends in Hierarchical Taxonomy Displays

Taxonomies connect users to content. So, how a taxonomy is displayed to users is very important in its effectiveness. This is a topic about which I gave a conference presentation back in 2011 and will present again next week. As I update my previous presentation, looking at some of the same public websites with taxonomies, I have observed some changes that might be considered as trends.

While faceted taxonomies (used to filter/refine/limit results by certain criteria with choices of taxonomy terms) have become more common on ecommerce or other database websites, they are not suitable in all circumstances, and when a taxonomy has a large number of topical terms, a hierarchical arrangement of those topics might be better.

Displayed full hierarchical taxonomies, however are more difficult to find. They are not as often the default.  Some have disappeared entirely such as the Yahoo directory, which was discontinued in December 2014 after 20 years. (Admittedly, trying to classify as many websites as possible into a hierarchy, as the web keeps growing, is a never ending task.) In other cases, the search box is more prominent on the page, and the link browse categories needs to be hunted for.

In the past, I had observed two main different kinds of hierarchical displays: one-level-per-page and expandable hierarchies with plus signs. The first has evolved, the second is has become rare, and a third method has emerged.

One level of taxonomy hierarchy per page was the design of the former Yahoo directory and had been early on the style followed on other sites. An example that closely follows the Yahoo Directory, is the dmoz/Open Directory Project. A list of category labels or topics at each level takes up the entire screen/page display, without the display of other content. Displaying additional content on every page has become important, so hierarchical taxonomy categories now tend to be confined to more compact lists to free up space on the web page for content. This works for some taxonomies, not all. Meanwhile, a list of terms at the same level that take up the entire page is a style that is rarely followed anymore.

Expandable hierarchy “trees,” typically with plus signs next to topics to expand a topic’s subcategories has become quite rare, at least in public web sites. An example are the USA Today topics. This hierarchical taxonomy design had been developed based on the recognizable desktop file folder structure, such as in Windows. In the meantime, users have become familiar with different representations of topic hierarchies on the web, so mimicking expandable file menus is no longer the only way to engage users. Expandable topic hierarchies are not as easy to update and change on websites and, it can take a long time to load the web page. Expandable hierarchies allow the users to have more than one hierarchical level expanded at once, which facilitates exploring the taxonomy. As much as we taxonomists might enjoy browsing a taxonomy, the goal is to get users to content rather than have them spend time exploring the taxonomy.

A third method of displaying multiple levels of a hierarchical taxonomy is through “fly-out” subcategory lists. Examples include Lynda.com (under "Browse the Library") and Books & Authors. I had not noticed this method before, so it seems to be a new trend. They are similar to submenus in website navigation, but rather than for website navigation, the topics are linked to indexed content items, which are listed in a result set for each subtopic. Fly-out subcategories allow the users to still see the parent category list, if the user wanted to back out to it, like in an expandable tree hierarchy. But unlike an expandable tree hierarchy, you cannot have multiple parent categories expanded at the same time, which is not that important anyway. The fly-out subcategory style is thus a positive trend in hierarchical taxonomy displays.