Geography Reference
In-Depth Information
6.2.2 Attention-Based Principles and Cartographic Symbology
Unique to a situation such as ambulance command and control or air traffic control
is the fact that any interface should have the capability of representing (infrequent)
abnormal events as well as (routine) normal events. In terms of a dynamic map,
manipulation of animation cartographic variables (MacEachren
1995
) to control
the behaviour of symbols on a map can ensure that the ephemeral abnormal events
do not get lost against the background of normal events. For example, combined
use of the duration and frequency variables can create a ''blinking'' feature that
draws attention to itself by cyclically switching itself on and off (e.g. Fisher
1993
;
Kardos et al.
2006
). Similarly, use of longer or shorter phases than normal or
altering the order of animation can attract the eye with abnormal events.
Of course, static cartographic variables such as colour (hue, saturation, value),
texture, orientation, shape, size, arrangement and focus (Bertin
1983
) can be used
in the same way. As an illustration, there may be a cartographic reason for the
anomalous result in trial 24 of the MLD study. Focusing on the symbol used for all
static and dynamic objects, the shape is the function of a unified arrowhead and
text label, whether used to represent ambulance, ambulance station, or other.
Crucially, this means that a lengthy label (such as with the target incident in
Fig.
6
) means a lengthy symbol as a whole, increasing the importance that the
attached arrow feature indicates where the actual location is. The label in question
almost bridges the harbour, which may be causing ambiguity at first glance as to
which part of the harbour it is actually pointing to (exacerbated by the arrowhead
being dominated by the label). Shifting emphasis towards the point itself, which at
the moment is only implied, and lessening the prominence of the label, though not
too much so as to jeopardise the purpose of the display, would be a cartographic
solution for this scenario (e.g. to use graphic variable terminology, a small circular
shape, but in a vivid hue is required—depending on the identity of the object).
Returning to Wickens' principles of display design (Wickens et al.
2004
), such
a multimodal display is implicit in one of the attention-based principles (that of
multiple resources) and principles that aid the perception of the user (avoiding
absolute judgment limits by engaging more than one sensory variable). A variation
on this satisfies one of the other perceptual principles, design for redundancy gain,
expressing a feature in more than one form (e.g. major roads are exaggerated and
have vivid colours, to make them noticeable).
These visual cartographic solutions to display both abnormal and normal sit-
uations on a dynamic map are the equivalent of a compromise display in interface
design terms (Wickens
2000
), acknowledging that it is difficult to address both
situations on the same display. A solution could be a dual display (Wickens
2000
),
but this may increase the cognitive demands placed on operators, especially where
integration is involved. With its two screens, the MLD display is closest to this
category, with the added benefit of superimposition lessening the cognitive load.
This only works through the shared simulated geography of the two screens, a
spatial overlay association between the two layers that aids the cognitive process
yet further.
