Dynamic Interaction and coordinated views

Interactive and dynamic properties o f visual representations may give users the experience o f being in direct contact with the data (Ware 2000). “Interaction techniques allow dynamic changes o f the visualization according to the exploration objectives, bu t they also make it possible to relate and com bine multiple independent visualizations” (H innenburg et al. 1999: 24). Allowing users to relate visualizations has been identified as an im portant feature o f

effective inform ation visualization (Haslett et at. 1991). For instance. N orth and

Schneiderm an (2000) have pointed at how multiple coordinated visualizations enable the rapid exploration o f complex inform ation and improve user performance. Therefore, data objects or different attributes o f one row or database record often appear in m ore than one display view. Nevertheless, these various graphical displays m ust be related in some way so as to allow the user to interpret the complementary inform ation that the representations provide.

Brushing is a technique which utilises the dynamic highlighting o f all the objects in visual displays that correspond to the same record in a dataset (Cook et al. 1997; M onm onier 1989; Becker and Cleveland 1987; M acDonald 1982). T he first reference to brushing is attributed to N ew ton (1978) w ho defined brushing as interactively changing the representation o f a group o f points to a unique colour or symbol. In other words, when a group o f data objects is highlighted in one graphical display, brushing allows highlighting o f the same group in all other views in which they appear. Figure 2.5 shows an example with three data views: a map, a scatterplot and a parallel coordinate plot (PCP). The three graphic displays show attributes from a geographical dataset. N ote that a set o f objects was selected on the scatterplot and highlighted in Hght blue. Using brushing, all corresponding objects are highHghted in each o f the linked views using the same colour, which facüitates relating the inform ation provided by each graphical display (M acDonald 1982). Thus, the technique allows the investigation o f multivariate data as different attributes can be explored simultaneously.

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Figure 2 3 Brushing and linking views with geospatial data

Dynamic querying (Williamson and Shneiderman 1992) is a technique that allows users to perform structured queries on-the-fly using graphic devices such as scrollbars. Each scrollbar in Figure 2.6 (R i^ t) represents one attribute in a dataset. By dragging the ends o f any o f the scrollbars, users can interactively manipulate the limits o f the attributes o f data records and, in that way, the num ber o f data objects that are visible in a graphic display. N ote that in the example o f Figure 2.6, three scrollbars have been manipulated so that only records within certain value ranges for the three attributes are visible in the PCP. If the response to the dynamic query occurs in near real time, the technique allows users to pose and solve questions concurrently, as they can manipulate the graphic device and see the result o f the operation at the same time. Tobon (2003) describes an environm ent that implements these devices in a geospatial domain, which is also discussed in detail in Chapter 4.

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Figure 2.6 Parallel Coordinate Plot (Left) and Dynamic Query devices and Details-on- Dem and (Right) in DecisionSite (Spotfire, Boston)

Details-on-Demand (Ahlberg and Shneiderman 1994) is a technique by which details o f all attributes associated with a particular data object may be required by the user. Figure 2.6 (R i^ t) shows an example where the specific values o f attributes in a record o f interest are queried. By clicking on the object in the graphic display, the Details-on Demand window is populated with the relevant information. This concept has also been implemented as off-the- shelf functionality in many GIS packages. Figure 2.7 shows an example from ArcGIS (ESRI, Redlands). By clicking on a spatial object, all attribute values associated with its corresponding record in the database may be presented to the user. This technique is useful in data exploration for a num ber o f reasons including assessing the relevance o f selected subsets o f data objects when the user is trying to address some task or reach an answer to a particular problem scenario.

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Figure 2.7 Details-on-Dem and in ArcGIS (ESRI, Redlands)