Navigable Spaces

Examples:

The WWW and other hypertext systems
Myst
Museum exhibit in a set of physical rooms
Set of applications in a suite, as with the PalmPilot or a network computer

Context: The artifact contains a large amount of content -- too much to be reasonably presented in a single view. This content can be organized into distinct conceptual spaces or working surfaces which are semantically linked to each other, so that it is natural and meaningful to go from one to another.

Problem: How can you present the content so that a user can explore it at their own pace, in a way which is comprehensible and engaging to the user?

Forces:

The user wants to know where they can (or should) go next, and how it's related to where they are now.
The user wants to be able to choose where to go next.
The user doesn't want to get lost.
The concept of information spaces is a natural one for people to think about, both because it mirrors the real world and because the WWW is so commonly understood.
It's delightful to explore a new place, where the user doesn't necessarily know what's "around the corner."

Solution: Create the illusion that the working surfaces are spaces, or places the user can "go" into and out of. Start out with at least one top-level or "home" space, to which the user can easily return (Clear Entry Points). In each space, clearly indicate how you get to the next space(s), such as by underlined text, buttons, images of doors, architectural features, etc. Use the spatial locations of these links to help the user remember where the links are. Provide a map of how the spaces are interconnected (Map of Navigable Spaces), preferably one that allows the user to go directly to the spaces represented on the map. Make sure that the user can easily retreat out of a space (Go Back One Step) or return to the home space (Go Back to a Safe Place). Illustration of "Navigable Spaces"

The user will build a mental model of the content from the structure of the Navigable Spaces. Therefore, construct the spaces and their interconnections to mirror the model you want to present (which may not be the same as the actual underlying data structure). Chains, trees, and star patterns are common ways to structure Navigable Spaces (see illustration below); they are easy to understand, visualize, and navigate, and they can contain rich content.

Resulting Context: As pointed out above, Map of Navigable Spaces should be one of the first patterns you deal with, even if you explicitly choose not to use one; the same for Go Back One Step and Go Back to a Safe Place. To help show where the links are in the spaces, you can use Pointer Shows Affordance; to give additional information about where they go, use Short Description.

People using the WWW tend to depend upon their browser's Interaction History (the links you've most recently visited, in chronological order) to get around. Not surprisingly, they also depend upon their Bookmarks to keep track of places they want to go back to. These two patterns might be especially important in any large or unbounded set of Navigable Spaces, particularly if a map is impractical.

When you're dealing with power users, seriously consider the value of displaying more than one surface at a time, perhaps using Tiled Working Surfaces. It's often good to provide the user with the option of being in at least two or three spaces of their choice, especially if a user is likely to be jumping between spaces frequently. This does increase the user's cognitive load, though, so it may not be appropriate for simpler artifacts that require short learning curves.

Notes: With games, part of the fun is in figuring out where you are and where you can go next, so maps and obvious links would actually reduce the user's fun. In a way, the WWW is similar -- who could ever make a map of the WWW anyway? -- but, of course, not everyone uses it for fun.

Notice that chains are structured similarly to Step-by-Step Instructions, trees to Hierarchical Set, and stars to Central Working Surface. All three of these archetypes have very strong, simple geometric properties; they probably warrant further exploration.

Comments to: jtidwell@alum.mit.edu
Last modified May 17, 1999