In spite of affordability, portability, and convenience of mobile handheld devices, there are a number of usability problems associated with Web access through those devices, largely attributable to their inherent physical constraints.
We discuss the reasons for these observations and suggest ways in which limitations of SDAZ in the small-screen context may be overcome. Some SDAZ users became lost within the information space and were unable to recover navigational context. For navigation in two dimensions (map browsing) SDAZ supports more accurate target location, and also produces longer task completion times. In fact, for one-dimensional navigation (vertical document navigation) the normative interface out-performed SDAZ. However, the reduced screen space reduced the impact of SDAZ in comparison to that reported in previous studies. Users responded positively to the system, particularly in relation to reduced physical navigational workload. In this paper, we propose algorithmic extensions to the technique for application on small-screen devices and present a comparative experimental evaluation of user performance with the system and a normative scroll–zoom–pan interface. Previous research indicated dramatic user performance improvements when using the technique for document and map navigation tasks. SDAZ combines zooming and panning facilities into a single operation, with the magnitude of both factors dependent on simple user interaction. Speed-dependent automatic zooming (SDAZ) has been proposed for standard desktop displays as a means of overcoming problems associated with the navigation of large information spaces.
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