In contrast to the communication model of cartography, the visualization model of cartography is relatively new and still evolving. Currently there are very few rules, procedures and consensus governing the process of cartographic visualization. Instead the emphasis is upon the user's own personal preferences, ideas and agendas with the aim of discovering something new (and hopefully interesting) about the world. The purpose of cartographic visualization is to facilitate data exploration, allowing the data to be investigated for unknown relationships, to reveal patterns, to flag unusual events and outliers and to generally support inductive reasoning and hypothesis generation. Cartographic visualization is seen by many geographers as the only means by which increasingly large and complex digital spatial datasets can be analysed effectively.
The key to cartographic visualization is the high degree of interaction and dynamism afforded by computer technology. Cartographic visualizations allow panning, zooming, rotation, dynamic re-expression, dynamic comparisons and brushing as part of their functionality (Dykes, 1997). Panning, zooming and rotation allow the user to navigate around the map, change the orientation of the map in three dimensions and increase or decrease the scale at which the map is viewed. Dynamic re-expression allows the map to be updated automatically when a change has been made to the dataset. Dynamic comparisons allow the map to be linked to different views of the data, such as a table, a graph or another map. Choosing a point in one view will highlight the same point in the different views. Brushing allows users to select areas by dragging the mouse across the map. These functions are useful in the exploratory analysis of spatial data, particularly when not much is known about the nature of the data. The Cartographic Data Visualizer (cdv), shown in Figure 11.3, is an example of recent software that allows exploratory spatial data analysis using an interactive map as the platform (Dykes, 1998).
Cartographic visualization has also benefited from new dynamic visual variables complementing the existing set of visual variables used in traditional cartographic design. These new dynamic visual variables include animation, multi-media and virtual reality. Animation allows movement on the map, which can be useful when exploring changes through time and across space. For instance, it can be used when investigating flow data such as migration patterns or the movement of water through river channels. Animation can also depict the growth and change of city structures or vegetation cover in upland areas. Multimedia are the use of more than one medium such as photographic images, video footage, text-based data and even sound to represent and convey information (Cartwright, 1999). This qualitative information can provide context and meaning to a traditional cartographic representation. It allows the map user to see, hear and perhaps experience what a place is like rather than relying upon traditional abstract and (typically) statistical representations.
Virtual reality is an exciting prospect, although its impact on cartographic visualization is still unclear. An example of its use in geography and cartography has been the creation of Virtual Worlds (Fisher and Unwin, 2002). Virtual Worlds is a cheap and simple version of virtual reality that has been used to visualize landscapes within multi-user environments and usually on a PC. It does not involve the creation of a three-dimensional model of reality within which a viewer is immersed, but instead uses linked images to produce a 'through the window' navigable scene. The use of perspectives and user navigation allows an adequate impression of the virtual environment to be maintained. In geography Virtual Worlds are best known within the context of Virtual Field Courses that are used in teaching and learning contexts (Dykes et al., 1999). Virtual Worlds have also been used in the visualization of the built and natural environments in which users can fly through actual or planned three-dimensional landscapes. This is becoming an important feature in urban planning and resource management, allowing the user to explore the outcome of different scenarios upon existing landscapes.
The growth of the Internet has also had major impacts upon cartographic visualization, fostering the development of web-cartography (Kraak and Brown, 2001). The Internet's interactivity and flexibility have enabled mapping on demand (Cartwright, 1997) and there are a number of websites that allow people to log on, design and download their own maps. The Internet's highly graphical nature, its ability to support multimedia, animation and virtual reality also means that it is an ideal medium for producing cartographic visualizations.
Web-cartography is seen as a way of democratizing map making with visualization providing a common language enabling the collaboration of different groups of people in interactive, learning multi-user environments (MacEachren and Kraak, 1997).
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