Usability Principle #5: Proximity
By the time we arrive at this principle, we should have already determined that the feature or feature set in question is 1) a necessary part of the overall design, and 2) not completely hidden by automation. What should we consider next?
Because no one seems to read user manuals anymore (did we ever?), a fundamental tenant that most usability professionals espouse is the idea of interface “discoverability” — some pathway whereby we learn as we go. Discoverability has many manifestations (menus; “tip of the day;” Clippy, the much maligned MS Office help assistant), though I have to admit that I am not a fan of most. While I agree with discoverability in principle, I find that many of the features that are designed to make user interfaces discoverable to novices get in the way of expert users. As a result, designers have struck upon the idea of having different interfaces for people with different experience levels (i.e., “normal mode,” and “expert mode”). Oh what a tangled web we weave…
The question remains, then, how can we encourage simple discoverability? I believe the answer lies in one facet of a principle that has even wider design implications, something I will call “proximity.”
Proximity refers to the idea that controls should always be as close to the action as possible. Proximity can apply to physical space (for example, transport controls for a movie or song appear just below or even superimposed above the play window), but also in terms of a clickpath, collapsible tree structure, or menu cascade. In fact, usually the second type of proximity is more important than physical proximity, because burying controls on separate screens or underneath other piles of controls means obscuring options.
I would like to illustrate with two examples — one good and one bad — from Apple’s iPhone. First for the bad. By now, pretty much everyone has seen what the home screen on the iPhone looks like – black background, square application icons with rounded edges laid out across four columns, with application names displayed underneath. There are three rows of icons up top, and then a special row of icons along the bottom of the screen, but based on the layout, there is room for another row of icons in between these. Here’s what bothers me: in order to access Contacts, we have to click on the Phone icon first, and then choose contacts from one of the five available icons inside the phone application. To me, this doesn’t make any sense. First, I often use my contacts for other things – to look up an address, to send an email, to send a text message. Why can’t I start from a contact and then go into one of these other applications? Second, there is that annoyingly empty row on the home screen, which would be a great place to plop down a Contacts icon. In fact, for the iPod Touch (where Apple seems to be in search of some applications to fill up that empty black space), Contacts does appear on the home screen. Perhaps even worse than Contacts being hidden away, Favorites is equally inaccessible. Whereas on virtually any other cell phone dialing a favorite means punching and holding down a number key, on the iPhone it takes me at least three (often four) taps (slide to unlock, phone, favorites, select favorite). Ugh.
Here’s one that I like better. Watching videos on the iPhone is great — for a mobile device the screen is large and bright, resolution is good for the size, battery life is decent, and the interface is elegant. When you choose a video to watch, the display automatically switches to a horizontal viewing mode, and the video fills the entire screen. Here I don’t mind tapping once to display the video controls – with the entire screen filled, it is natural for me to tap the screen if I want to do something. When I do, I get everything I need – a clock and battery gauge appear along the top; play, fast forward and rewind buttons are superimposed over the bottom third of the screen (large enough to tap easily); there is a scrubber below the clock that shows time elapsed and time remaining, and another button (oddly named “Done”) allows me to exit the video and return to the iPod menu. If I do nothing for a few seconds, the controls fade out harmlessly, or if I am impatient I can tap the video to hide them immediately.
Perhaps some will feel that I am bending my own rule to allow tapping the video screen to display the controls. I consider this a reasonable tradeoff. After all, one of the arguments that curmudgeons will make against proximity is that there is not enough room on the screen to make all the controls available at once. Of course not — we have to make some allowances. I certainly do not want to lose any of the screen real estate on my mobile device in order to persistently display transport controls or the clock. The important thing is that we add as few extra layers as possible. And when we have more than one layer, or when there is some separation, that we thoughtfully place the less important features farther away (or, we could go back to our minimalism roots and eliminate those less important features altogether).
Proximity has other implications in design, as well. Grouping controls that have affinity, displaying appropriate options based on context, and duplicating controls for convenience are some examples. But the best part about proximity is that it improves the interface for both novices and experts alike.