Database Reference
In-Depth Information
By interacting with the display, it is possible to explore not only direct
transitions between locations but also longer sequences of visited locations.
When the user clicks on a bar segment, the movements of the corresponding
subset of objects are highlighted in the display (i.e., shown by brighter colors). It
is possible to see which locations were visited and when. Thus, we can learn that
from the 994 cars that were in the center in the interval 500 (i.e., in the middle
of the trip time) 489 cars were in this region during the whole time and the
remaining cars came to the center mainly from the northeast (133), southwest
(132), northwest (74) and southeast (62) in the first 2 percent of the time. At the
end, these cars moved back. Analogously, the user can click on bands connecting
segments to select the objects participating in the respective transitions and trace
their movements.
8.5 Investigation of Movement in Context
The spatio-temporal context of the movement includes the properties of different
locations (e.g., land cover or road type) and different times (e.g., day or night,
working day or weekend) and various spatial, temporal, and spatio-temporal
objects affecting and/or being affected by the movement. The methods discussed
so far seem to deal with movement data alone and not address the context of the
movement, at least in an explicit way. However, the context is always involved
in the process of interpreting what is seen on visual displays. Thus, the analyst
always tries to relate visible spatial patterns to the spatial context (e.g., the
highest car traffic density is on motorways) and visible temporal patterns to the
temporal context (e.g., the traffic decreases on weekends).
The cartographic map is a very important provider of information about spa-
tial context; therefore, maps are essential in analyzing movement data. It is not
very usual, although it is possible, to include information about temporal con-
text in temporal displays such as a time graph. A space-time cube may show
spatio-temporal context, but occlusions and projection effects often complicate
the analysis. Besides the context items that are explicitly represented on visual
displays, the analyst also takes relevant context information from his/her back-
ground knowledge. Visual displays, especially maps, help the analyst in doing
this since things that are shown can facilitate recall of related things from the
analyst's mind. After noticing a probable relationship between an observed pat-
tern and some context item, group of items, or type of items, the analyst may
wish to check it, which can be supported by interactive visual tools.
The analyst may not only attend to the movement context for interpreting
results of previously done analysis. It may also be a primary goal of analysis
to detect and investigate particular relationships between the movement and a
certain specific context item or group of items. For example, the goal may be
to investigate how cars move on motorways or in traffic congestions. To do the
