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Choosing the scale and extent of maps for navigation with mobile computing systems

Unlike most paper maps used for navigation, digital maps when displayed on handheld, personal navigation systems do not show the entire mapped extent in a single view, nor are they limited to a fixed map scale. The mapped extent, or footprint of the earth, that appears in any given view is dictated by scale, and there are as many scales as zoom steps. But what drives the choice of scale? We investigate this question first through an assessment of currently available navigation systems, to analyse the consistency or variation among current practices. The vast range of scales and zoom steps found across six software packages indicates an absence of design guidelines, the consequence of which is that users will have a very different experience, with respect to the map, depending on what program they use. Since map representation has been shown to influence spatial behaviour and decision-making, such differences arising from map scale may lead to unintended consequences for navigation system users. We argue that meaningful scales and map extents that incorporate temporal and behavioural aspects of travel as cued by global position system (GPS), can actually convey relevant information to map users. Drawing upon time-geography concepts and real-time data from GPS signals, we explore time-scale bars and isochrones as potential methods of spatiotemporal information delivery to users of personal navigation systems.