Geography Reference
In-Depth Information
datasets. However, it is difficult to design intuitive and useful difference modules. Layering is
used in geographical visualization; for instance, different land uses can be layered on top of
each other and these layers can be separated in space or time such that the user can explore
information on individual layers. However, it can be difficult to perceive the information
comprehensively on each layer due to the occlusion of one layer to another. It is possible
to imagine other strategies to merge the data, such as incorporating different information
through various graphical lenses (Tominski
et al.
, 2006), but most general geovisualization
systems do not support such operations.
3.4.2 Interactive filtering
Interactive filtering is an important exploratory technique. The user changes a parameter,
or the range of values, to reduce the quantity of information that is being displayed. What
once was a dense, overpopulated display can clearly display trends and highlight important
outliers. Methods range from constraining ranges (Williamson and Shneiderman, 1992) to
changing the bin width of a histogram (Theus, 2002). One important aspect of this type of
interaction is that the query immediately updates the display.
Dynamic queries
originated from work done by Ahlberg, Williamson and Shneiderman
(1992). There are many examples where dynamic queries have been used to display geo-
graphical information. HomeFinder (Williamson and Shneiderman, 1992) demonstrates
how geographical information, in this case houses for sale, can be explored through
dynamic queries; IVEE (Ahlberg and Wistrand, 1995), which was later developed into
SpotFire
TM
, demonstrates how heavy metals in Sweden can be explored using dynamic
queries; Dang, North and Shneiderman (2001) show how choropleth maps can be used with
dynamic queries; Burigat and Chittaro (2005) present interactive queries for geographic
data on mobile devices. Range sliders can be directly integrated with the visualization;
for example, researchers have placed range sliders directly upon parallel coordinate plots
(Shimabukuro
et al.
, 2004). They have also been incorporated into many general geovisual-
ization tools (e.g. Andrienko and Andrienko, 2003; Brodbeck and Girardin, 2003; Feldt
et al
.,
2005).
3.4.3 Interactively adapting mapping parameters
Colour is important in geographical visualization. In fact, changing how colour is mapped
to the display can considerably alter how the information is perceived. Not only can a colour
map affect whether a colour-blind person can perceive the information, but elements may
be hidden or emphasized through different colour mappings; colour can permit the user to
perceive depth and can be used to delimit areas and borders. It is well known, but infrequently
applied, that certain colour maps, such as the rainbow colour map, may mislead the user
(Rogowitz and Treinish, 1998). Hence choosing the correct colour map with an appropriate
transfer function is important (Brewer
et al.
, 1997; Rogowitz and Kalvin, 2001). Colour itself
isonetypeof
visual variable
, thus it is often be possible to exchange colour with another type
(such as grey scale, size or texture). However, it is prudent to exchange the visual variable
with one with similar traits, such as exchanging one visual variable that displays continuous
data with another that is also perceived continuously (Bertin, 1981).
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