Small User Interfaces Do Not Scale

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The mobility of users—their mobile interaction with the portable terminal and their consumption of information and entertainment in mobile situations—makes a difference in user interface design. A mobile user interface is not a miniaturized desktop UI.

In particular, the small user interface does not scale down. When adding features and squeezing them into the device, developers face a usability “knee” (Figure 1.5). That’s the situation where the UI starts to become too packed; in principle, new features can be accommodated, but in practice they would not be very usable any more. There is a limit in the density of a user interface; a menu structure, a screen resolution or an icon of given size has an inherently limited human-machine communication bandwidth.

Applications require a minimum screen space to be usable. When the screen size decreases, one cannot simply keep compacting the presentation, but instead the whole structure of the user interface must be reconceived. In a calendar application, the concepts of a monthly or weekly view make no sense if the screen does not allow for displaying the dates and a certain amount of user-defined information about the entries. At that point the metaphor needs to be changed from “calendar” to “list of reminders,” for instance. Applications have to be optimized for small screens on all layers of the interface: the vocabulary layer, the logic layer, and the layer of functionality.

A causal relationship obtains between portability, user needs, and the details of the UI. Portability implies requirements concerning, for example, size, one-hand operability, and usability in multiple task situations. These specifics influence the selection of user interface hardware components and input solutions. With limited screen size and key count, any presentation of alternative options has to be sequential; only a few items can be presented at a time. Prioritization then becomes crucial, as the most-needed options have to be among those presented first.

In every situation, creating approachable and easy-to-use interfaces depends on nothing so much as the priority of functions. In the case of basic phones, the top-priority user action is often close to self-evident—there may be just one thing that’s really necessary while all the rest are secondary options. One key may be enough. On the other end of the complexity continuum, mobile terminals are used to access the same content as desktop environments with full-size keyboards, large displays, and broadband connections to the Internet.



Mobile Usability(c) How Nokia Changed the Face of the Mobile Phone
Mobile Usability: How Nokia Changed the Face of the Mobile Phone
ISBN: 0071385142
EAN: 2147483647
Year: 2005
Pages: 142

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