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Article Excerpt
Introduction
Understanding how users interact with digital maps on handheld devices such as personal digital assistants (PDAs) and cell phones is critical for creating effective maps for mobile computing. Digital map displays allow users to zoom in and out, to add or remove data layers, to change the appearance of the display, and, with geographic information systems (GIS), even to modify the dataset itself. New capabilities resulting from mobility--which range from the ability to interact with data to taking complex datasets into the field--give greater flexibility to maps and mapmakers. How people use these capabilities while actually engaged in mobile activities, whether as a sightseeing tourist or data-collecting researcher, needs to be understood in order to inform map design for these devices.
This research reports on a study that examined subjects' performance during an on-foot navigation task with a handheld computer. Subjects followed routes marked on maps at two different levels of generalization, an aerial photograph and a classified, simplified version of the aerial photo. One focus of the experiment was to evaluate the level of map generalization with regard to three dependent variables: time to route completion, amount of map browsing, and accuracy in following the route. A second focus considered subjects' spatial abilities, familiarity with the study area, and experience with maps and mobile technology. Examining these factors with subjects' performance begins to address questions regarding user behavior with maps on handheld devices. How does a person's spatial ability influence how he or she interacts with a map? Are there consistencies in the types and amounts of errors that people make, and how is error related to individual differences? There are a variety of factors that affect how a mobile map is used, as well as a large variation in the way individuals interact with a digital map on a handheld device.
The methodology and results from this study inform other contextual frameworks by assessing patterns of behavior with subjects of different spatial abilities and experience using maps of varying representation in a controlled experiment. The results are specific to the type of environment of the study area and the activity of route-following, and would likely be different if the experiment were replicated in a different type of area, such as a downtown city center or a forest, with a different sized study area, and if subjects were finding their way to a destination point rather than following a given route. Systematically considering maps in a variety of contexts is a necessary step towards a more complete understanding of how people interact with maps while mobile. This knowledge will inform generalization techniques, such as in determining just what level of detail is necessary, or to what extent features can be aggregated or simplified to fit on the display and still be useful.
Related Research
This study complements continuing research on spatial information delivery for mobile devices, and it is unique in considering controlled variations of map generalization in a field-based task with a digital map. It is intended as the first of a series of studies to systematically test carefully controlled variations of representations to determine what makes effective mobile cartography, and why.
Dynamic, digital maps are key applications for mobile devices, especially for providing navigation assistance to non-expert users, or assisting scientists and others who work with spatial data in the field. A recent special issue of Cartography and Geographic Information Science dedicated to mobile mapping and GIS identified a research agenda for mobile GIS, encompassing the areas of infrastructure, data, and user issues (Clarke 2004). A major research area in this agenda is navigation assistance and location-based services. Prototype navigation aids, both handheld and wearable varieties, continue to be developed and tested. Commercial products, such as in-car navigation systems, are already available to consumers. Research has not kept pace with the technology, however, even for digital maps for standard-size computer monitors; there are no cartographic design guidelines yet for digital maps as there are for traditional paper ones (Meng 2003). There is a growing body of research investigating the variety of spatial information presentation available for handheld and wearable mobile devices: visual maps in 2D and 3D, text/audio descriptions, schematic diagrams, ground-view photography or video, or combinations of these. A review of these systems is beyond the scope of this paper (Urquhart et al. 2003 provides an overview of major projects), but many of these studies are concerned with how well a navigation system works as a whole, on a technological or usability level, such as which representation type or modality is more effective, rather than trying to determine why one representation method is better in light of how users interact with the information.
Map generalization research for small display is faced with the technological challenge associated with the limited screen space of mobile devices, and it is driven by the need for automatic methods of creating representations that can adapt to the user's context (Edwardes et al. 2003), or can change scales and levels of detail in real-time (Hampe and Sester 2002). One of the primary problems of automatic generalization is devising a way to represent only that information which is relevant to the user at a particular time (Agrawala and Stolte 2001). The question of what that relevant information is remains to be determined.
A conceptual framework for approaching what information is important to represent on a mobile map has been developed by a number of researchers based on the context of the user and the mobile device. As a starting point for designing spatial representations, "context" identifies the need for different types of information for different users and activities, and the need is met by the dynamic capabilities of digital graphics. As a result, the amount and type of information displayed on the map can be custom-tailored to individual users (Reichenbacher 2004). Nivala and Sarjakoski (2003) discuss mobile map context from the broad, mobile computing context categories of Computing, User, Physical, Time, and History, defining more specific categories related to maps, which encompass hardware and infrastructure and how, where, and by whom the map on the device is used. They emphasize a need for research to determine which context factors are most important to incorporate when designing a map, and how exactly to do it (Nivala and Sarjakoski 2003).
Considering navigation systems specifically, Hampe and Elias (2004) focus the idea of context on the user, his or her navigation purpose, and the situation: individual characteristics of spatial skills, experience and familiarity with the area; whether he or she is moving by car or bicycle or on foot; navigation style preferences; and characteristics of the situation, such as the time of travel, season, traffic conditions, etc. These factors are taken into consideration to determine the best way to present navigation information for a given context, such as which landmarks are going to be relevant, and which presentation modality fits with the attention and interaction limitations of the user (Hampe and Elias 2004). The information upon which this framework depends, especially as regards how users' abilities and experience affect the way they use mobile maps, still needs to be determined.
An extensive framework of context for mobile cartography has been developed by Reichenbacher (2004) and is largely concerned with the adaptive nature of maps on mobile devices. This approach emphasizes that the information content for the map (such as area extent and level of detail) and the information visualization (scale, generalization, symbolization, etc.) are categories in which elements can be presented in a specific and optimal way for a user and his or her situation (Reichenbacher 2003). Reichenbacher (2004) reviews current approaches and outlines several specific research directions for mobile cartography.
Methods
In order to evaluate map generalization for handheld computer displays in a mobile context, an experiment was designed to have subjects use digital maps to complete a navigation task. The research subjects were 28 students, mostly graduate students, from various departments at the University of California, Santa Barbara (UCSB). Fourteen males and fourteen females participated, their ages ranging from 19 to 37.
Materials
Representations starting at the least-generalized end of a representation spectrum were chosen for this study: a photorealistic image and a manually created generalized map. A color aerial photograph at a scale of 1:12,000 was scanned to digital format and used as one display condition (Figure 1). Taken 14 months prior to the study, it portrays the actual environment in terms of detail and color, with no cartographic design applied. The generalized map is a classified and simplified version of the aerial photograph, digitized from the aerial photograph using a GIS. All readily distinguishable landscape features on the photograph were manually traced, then the polygons were color-coded according to feature type: buildings, sidewalks, grass and other vegetation, trees, paved roads, sand and water. The objective was to evaluate two representations that were equivalent in feature information, with the only difference in the level of generalization being a reduction of detail and classification of features.
[FIGURE 1 OMITTED]
The use of the aerial photograph for this study represents a baseline "map," or even a worst-case scenario in terms of map design, since there has been no design applied. In testing the photograph against a generalized version, the differences are attributable to the level of generalization, rather than...
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