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As of 2012, the size of a typical mobile phone screen is approximately3.5
2.25 inches and approximately 480
320 pixels. The small screen areaprovides relatively limited space in which to display content. Thus, designersmust pare down the user-interface content to ensure readability and to avoidcluttering the screen.Figure 7-13shows a sample mobile RMO Web page.Compared to the larger Web pages shown earlier, the mobile page eliminatesmany elements, including all images except a scaled-down logo. The remainingtextual content is abbreviated, and special attention has been paid to contrastand layout in order to ensure maximal readability.Small keyboards and touch screens also provide limited capabilities for userinput. Mobile device user interfaces must avoid detailed textual input wheneverpossible and must provide touch controls that are well spaced and easy tolocate. On many phones, speech-to-text capabilities provided by the phone’soperating system can be used to streamline data entry and navigation, althoughthe state of this technology still makes errors relatively common. Thus, designersmust not rely too heavily on speech recognition and must ensure that errors areeasily detected and corrected.As of 2012, most mobile phones include connectivity through cell phonenetworks and Wi-Fi. Most current cell phone networks, described as third-FIGURE7-13RMO Web page layout for amobile phoneassistive technologiessoftware (suchas text-to-speech and voice-recognition utilities)that adapts user interfaces to the special needsof persons with disabilitiesCHAPTER 7■Designing the User and System Interfaces207
generation (3G) networks, were originally designed for voice communication,with data communication grafted on as an afterthought. The throughput for 3Gnetworks is usually no more than one-tenth the throughput of a Wi-Fi network.In 2010, deployment of 4G networks began in the United States. 4G networksincrease data throughput to approximately that of Wi-Fi, although many userscompete for access to that bandwidth.Because mobile phone data throughput is much more limited than for othercomputing devices, the performance issues described earlier become much moresignificant design constraints. Page sizes must be limited to achieve acceptabledownload and page-refresh rates. High-resolution graphics are used only whenabsolutely necessary, and bandwidth-consuming video is typically avoidedentirely. For RMO’s mobile Web site, background graphics are completelyavoided and high-resolution images are only used when a customer wants toview product details.Some organizations deploy custom-developed apps that users can install ontheir mobile devices. Those apps run within a mobile operating system, such asthe iPhone OS, iPad OS, or Google Android OS. Each OS provides a toolkit foruser-interface developers and a set of development guidelines that ensure maxi-mal compatibility among apps. Whenever possible, user-interface developersshould use these toolkits and guidelines