Graphical Representations

in Data
A GIS has the capability to produce high quality graphical representations, especially maps, making it a potentially valuable support system for the process of spatial thinking in the K-12 context. However, users must be aware of and understand the importance of data quality. Profes. sional-looking final products may conceal data errors. These errors may be referential (i.e., an error in specifying something such as a street address), topological (i.e., a linkage error in spatial data such as an unclosed polygon), relative (i.e., an error in the position of two objects relative to each other), or absolute (i.e., an error in the true position of something such as a floodplain boundary not aligned with property boundaries) (Tomlinson, 2003). Currently, no GIS can automatically handle data error problems in a satisfactory manner. Moreover, products may be graphically misleading.

No GIS can guide K-12 operators in the choice of map symbols and other graphic effects. The process of exploring data on a GI S"produced map could be enhanced if users had real-time control over the visual display. Most information visualization systems provide user interface controls that remain "five" after the display is constructed. This enables users to change the appear. ance of features in the display interactively (e.g., a color ramp, a size control for point symbols, a transparency control for an image layer). Currently, GIS lack such a capability.

GIS provides poor support for the modeling of time (Peuquet, 2002) and related presentations via animation (MacEachren, 1994). Unlike animation systems such as Director and Flash that explicitly represent time (t) values, existing versions of GIS have no temporal "coordinate" as in x,y,t.
Although there are ways to work around this problem, achieved by stacking map layers in a temporal sequence of cross sections that can be refreshed several times per second (Goodchild,. 1988), they lead to a noncontinuous sense of time for users. Many important aspects of science and geography revolve around processes occurring through time (e.g., carbon and water cycles, glacial change, migration, urban expansion).

Although GIS lacks the capability to examine processes that occur continuously through time, technology exists for large-scale geospatial virtual representations of the entire Earth over time and in three dimensions. Keyhole Inc. Images provides users, even those with legacy computers, with access to terabytes of imagery and GIS files to view Earth as a three-dimensional object. Figure 8.2 shows screenshots of Farrhviewer, which allows users to zoom smoothly from a whole-Earth view to resolutions as detailed as I m and to "fly" over a realistic rendering of Earth's topography. The data to support these views are fed over the Internet, so a broadband connection is required foradequate performance. Farrhviewer and similar developments come close to the vision of"Digital Earth" outlined by former Vice President. Al Gore in Earth in the Balance (Gore, 1992). Larthviewer accommodates varying spatial resolutions, building its views dynamically from a patchwork of data obtained from various sources.

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This article was published on 2011/04/18