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Visualising Time
by Juan C. Dürsteler [message nº 180]

Visualising time or, best said, visualising the events that occur in time, is not so usual a topic. There aren’t so many visual metaphors associated to it either. We take a look at them here.
BusClock.gif (32521 bytes)
SpiraClock: An application that shows time as a spiral.
: Image as can be seen in its website.
Click on the image to enlarge it

Time is an elementary magnitude, a primary concept that can’t be defined in terms of other, more basic, concepts. As such its definition is difficult and it’s based on the universal human experience that time does exist and has certain properties. In other words, we have a very rudimentary knowledge about the nature of time.

You have only to look in any dictionary to realise that, in fact, we don’t have even the faintest idea of what time is except that it accomplishes certain features that (normal) people experience intuitively:

  • It’s apparently continuous.

  • It doesn’t have the same properties as space (should you look at the concept of “space” you’ll notice that we have no idea of what it is, either).

  • Events are bound to time (in fact the existence of events without time is impossible. We measure time as the interval between two events.

  • Events occur sequentially in time, that apparently runs in one privileged direction. We can’t run “backwards” in time.

These perceived properties of time condition the way we represent it. From a mathematical point of view, time could be represented as an increasing succession of real numbers.

The visual metaphors that represent time provide a framework to show the events that occurred in a certain moment of time. In one way or another time is associated to a (curved or straight) linear metaphor.

Let’s see the most frequently used of them.

  • Timeline. It’s a one dimensional graphic where temporal flow is depicted by a line (usually straight) where events are shown as markers whose location along the line is proportional to the elapsed time from a reference. Probably the first timeline was the outcome of the work done by Joseph Priestley in 1765 where he depicted bars above a line representing time to show the lapse of the lives of the “most distinguished men in the annals of fame”.

    Another clear example is the evolution in time of the Brookhaven Graphite Research Reactor from its installation up to its dismantling. Many timelines have a certain width or height to avoid the events overlapping. Unlike the temporal bands (see next), these widths don’t have any semantic contents.

    PriestleyBioChart.gif (71581 bytes) timelineBGRRFotos.jpg (65498 bytes)
    Biographic timeline by Joseph Priestley (1765)
    Source: As can be seen in the website "Milestones in the History of Thematic Cartography, Statistical Graphics, and Data Visualization" de Michael Friendly y Daniel J. Denis, York University, Canadá
    Click on the image to enlarge it
    Evolution in time of the Brookhaven Graphite Research Reactor
    Source: Image as can be seen in the BGRR website.
    Click on the image to enlarge it

  • Time band. In a time band the graphic is two-dimensional. One dimension is used to represent time while the other depicts a magnitude associated to the events represented. An example of time band is the Gantt diagram where tasks of a project are distributed in time

    Themeriver is another example of temporal band. Here the metaphor is that of a river composed of several streams associated to different topics of a collection of documents that are shown in different colours. Its width is proportional to the importance of that topic in a certain moment.

    GanttChart.gif (21965 bytes) themeriver675.gif (33167 bytes)
    Gantt Diagram
    : Made by the author using MS Project98
    Click on the image to enlarge it
    : image as can be seen in the website of the Pacific Northwest National Laboratory.
    Click on the image to enlarge it

  • Spiral. It is, in the end, a line (or band if we fill the space between rounds) that turns on itself . The advantage a spiral provides is two-fold:

    • It uses space more efficiently than a line.

    • When making it interactive, we can “extract” more information by unwinding it from its origin.

One interesting example is Sapplet, an interactive time representation in a way similar to the rings of a tree where SAP press releases appear related to important contemporary events.

SpiraClock is an elegant example of how the spiral metaphor can be useful even in tasks so simple as knowing the time our bus will pass or giving a compact visual information about our MS Outlook appointments. On the spiral a clock is overlapped. Its hands show the hour. We can move them back and forth to make the appointments or bus stops appear. The width of the spiral is controllable as the size of the clock is.

Sapplet1.gif (120605 bytes) Outclock.gif (145842 bytes)
Sapplet: Press releases and contemporary events as rings of a tree.
Source: Screenshot of the interaction with Sapplet as can be seen in its website.
Click on the image to enlarge it
Outclock: A version of SpiraClock that shows MS Outlook appointments.
Source: Screenshot of the program running in the author's computer.
Click on the image to enlarge it
  • Hélix: the 3D version of a spiral. It adds one more dimension to the representation of information. See for example the article "The Helix of Behaviour" to have an idea of its applications to the study of the behaviour of telephony services.

  • Dynamic representations. A way to show the passing of time between events is to use time itself, possibly affected by a scale factor, as an element of the representation. A clear example of that is a movie, where you are presented only with the relevant events of the narrative. The animation showing the multi million year collision between two galaxies in just a few minutes is also a form of temporal representation, although here the scale of time is implicit and it’s not shown explicitly in graphic form.

Representing the passing of time has its difficulties. Depicting space is relatively easy, since it can be bound to the concept of axis. An axis can be run in both directions and can appropriately reference the spatial dimension.

Time, nevertheless is not well represented by a line since it isn’t a spatial dimension and, moreover, it’s irreversible. Paradoxically, the widest used metaphor is that of the line. Maybe the key to it is considering time as just a state of space.

Links of this issue:

http://www.emn.fr/x-info/spiraclock/index.html   Spiraclock website
http://www.bgrr.bnl.gov/docs.html   Brookhaven Graphite Research Reactor website
http://www.math.yorku.ca/SCS/Gallery/milestone/index.html   Milestones in the History of Thematic Cartography... website
http://www.pnl.gov/infoviz/technologies.html#themeriver   Themeriver website
http://www.pnl.gov/infoviz/technologies.html   Pacific Northwest National Lab website
http://www.aec.at/annualreport/   Sapplet website
http://www.infovis.net/printMag.php?num=71&lang=2   Num 71 about The Helix of Behaviour
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