Geography Reference
In-Depth Information
The MLD achieves its effect by possessing a transparent front screen, capable
of presenting digital content that would appear as translucent to the viewer. There
are implications here for what is now possible with both symbology and gener-
alisation, as the extra display layer affords extra space, so should that mean room
for more symbols? A framework for the symbology of transparency is implied here
(the generalisation aspect is discussed in the next section), and should be subject of
further study. The study would set out to establish the visual qualities of super-
imposed feature type layers (i.e. testing all pairwise combinations of points, lines
and areas, including point-on-point, line-on-line and area-on-area) at a variety of
transparencies (defined by alpha value), also altering graphical variable levels (i.e.
different orientations, shapes, sizes etc.).
6.3 Other Factors
Another aspect of cartography that may arise in a command and control context
(though has not in the two case studies featured here) is composition. This includes
issues such as making sure the map as a whole is visually balanced relative both to
the screen extent and any other information content on the screen. This other
content may relate to the map (secondary elements such as legend, scalebar or
orientation) or be non-spatial information relating to the dispatch task.
The discussion above focuses on display issues, which may add to the overall
complexity of the dispatcher's task (other sources of complexity may be stress or
workload). By way of an overview, Endsley et al. (
2003
) characterised several
layers of complexity, from system (real world) complexity through operational
user perspective dependent complexity to apparent complexity. The latter com-
prises cognitive complexity (user's mental ability to deal with system complexity),
task complexity (i.e. of the actions to be taken) and display complexity. These all
affect how the user perceives the situation. Cognitive and display complexity are
especially pertinent to the cartographic process. Indeed, the link between the real
world (cognitive complexity is largely driven by the characteristics of the system)
and the map (or interface) representing it (display) is one of the central foci for
cartographic research, encompassed in choice of symbology and generalisation.
7 Conclusions
In this paper, we have seen a cartographic perspective applied to the results of
Human-Computer Interaction (HCI) studies on (pseudo-) geographic ambulance
dispatch displays. It was found that there was much overlap between the proximity
compatibility principle (PCP) and the interdependence with nearness that is innate
to all geographic phenomena. This is a real world facet that must be communicated
in representational displays to enhance their efficiency and effectiveness. That is, a
