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Proximity afforded by stacking the currents makes it easy to compare the
current shapes (smoothly bounded within the same time interval or across neigh-
boring intervals. We can see when two patterns match, when they complement
each other, or when they appear to be uncorrelated. We can also see when the
patterns are concurrent and when they are offset in time. The stacking order of
the currents is consistent along the full length of the river. The consistent use of
color and stacking order helps the user identify currents as the locus of attention
moves across the visualization.
3.3
Layers of Context
The ThemeRiver visualization includes the river of theme currents, a time line
below the river, and markers for related historical events along the top. Providing
such context allows users to evaluate content in relation to issues beyond those
contained within the documents themselves.
Figure 5 shows an interesting example of a related theme and event in the
sudden expansion of the 'oil' theme just before Castro confiscated American
oil refineries in 1960. On occasion we find patterns than cannot be explained
until further investigation uncovers events not included in our event stream. For
example, in a later period (not shown) ThemeRiver reveals the use of themes
'kennedy' and 'missiles' in March 1992. These themes seem outdated for 1992.
On further investigation of events in 1992, we discovered that Castro spoke in
March at a conference marking the 30th Anniversary of the Cuban Missile Crisis
(October 1962). In such cases we can easily add a marker to the event stream.
A user could also add analysis annotations in the same way.
Some additional elements of the ThemeRiver user interface help the user
in their analytical task. A histogram (Fig. 6, right) can show whether stream
content is light on a particular topic for a reason, or simply due to seasonal
causes (for example, the fact that less news is reported at the weekend).
In addition, showing multiple streams head-to-head can allow the user to
compare them (Fig. 6, left). Finally, tracking related themes is simplified by
assigning them to the same color family. This ensures that related themes appear
together and are identifiable as a group.
By associating a mechanism for collecting and simplifying data-streams with
a themed visualization tool, we shall be taking a step towards providing knowl-
edge workers with the types of tools they require for successful stream processing.
While this is certainly a step in the right direction, we are intrigued by the notion
of being subsumed by the data, being perceptually linked to its flow. For these
reasons we consider a third component, a means to engulf the user in the data.
4AmbentComponent
The key to developing the next generation human to information interface is to
move beyond the limitations of small computer monitors as our only view into
the electronic information space and keyboards and mice as the only interaction
devices.
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