Q: When is a hierarchy too deep, and what are the alternatives to using a deep hierarchy to access and organize information?
Hierarchies are often abused, plagued by issues that can lead to a frustrating user experience. Hierarchies can become overloaded, creating an Alice in Wonderland-like experience down a never-ending rabbit hole. Besides being tedious to navigate, deep hierarchies can take up valuable horizontal screen real estate. They can cause extra clicks to resize windows or force the user to guess at the truncated information. Large hierarchies can also introduce performance issues, taking several seconds to expand a single node.
When a hierarchy becomes overloaded, it’s time to examine the design of the user experience at a higher level. Ask whether there’s a better way to organize the information architecture or overall navigation scheme to take some of the burden off of the hierarchy. For example, some of the higher-level nodes in the hierarchy should be broken into separate navigation.
Another remedy to the overload dilemma is adding a drop-down or other filters that limit the information displayed by one or more attributes. For example, add a drop-down above a hierarchy that filters the information contained in the hierarchy by date or status.
A more sophisticated solution to improving the hierarchy experience is adding search functionality. Searching a hierarchy allows the user to drop into it at a deep level without having to make the entire trip down the rabbit hole. Searching can be as simple as a keyword match, or something more in-depth, like providing entire paths as a result set.
An example of this is eBay’s revised navigation paradigm for classifying items on their site. Previously, eBay users had to click through five or more levels to ensure that an item for sale was listed in the proper category. For example, suppose you wanted to sell a coffee press on eBay. To ensure that it was displayed in the right category, the user would traverse a path similar to this:
collectibles > home > kitchen > small kitchen appliances > coffee making > coffee press
The above example illustrates a seven-level hierarchy—and that’s for those who know what they’re doing. There are many decision points in categorizing an item that may cause the novice eBay user even more clicks. eBay’s new navigation adds a search paradigm on top of the hierarchy structure. Users save time by searching on the name of an item. eBay then suggests a categorization(s) or path for the item. The paths that best match are auto-assembled for the user. The user can choose a suggested path in its entirety, or customize parts of it.
There’s no hard and fast rule when using hierarchies. Their use really depends on the situation and the user audience. However, if users need to go more than three or four levels deep in a hierarchy, it’s worth examining other options.