Geoscience Reference
In-Depth Information
3.1.2 Graphic representation
3.1.2.1 Cartographical objects for self-orientation
Each group uses different objects for self
-
orientation. Users find their bear-
ings by locating different cartographic objects as shown in
figure 2
(“self-
orientation” line): vegetation, towns, hydrography, and roads. These
themes belong to the base map. Therefore, it seems legitimate to associate
(in reference to association relation of (Bertin 1967)) these objects visu-
ally. According to Bertin's theory, some visual variables are usable: shape,
size, hue, value, texture, orientation. In this case, it is impossible to use
neither the same shape nor the same size for all the objects because of their
variety. Moreover, value, texture and orientation are difficult to use
because they are not visible enough for objects that have very distinct surface
areas. In this case, hue is the most natural and the easiest visual variable to
use.
However, there are some rules for conventional colour use (Cuenin 1972).
For example, in Europe, forests and woods are traditionally symbolised by
green and hydrology by blue (Jolivet 2009). So there is a conflict between
these conventional colour rules and associating objects according to their
shared use.
Finally, we chose to stress the conventional colour rules: hydrology re-
mains blue and vegetation green. But all the other cartographical objects
that are used for self
-
orientation are associated because of their shared hue:
grey. In addition, to avoid inserting an order relation between these
objects, they will be represented with the same colour value. As a conse-
quence, the grey colour reduces the visual impact of all these themes. Thus
saturated colours are still available for more relevant themes (cf. section
3.1.1.2.).
3.1.2.2 Road theme
For these users, it is relevant to represent the road theme in grey (cf. sec-
tion 3.1.2.1.). Thus, the administrative hierarchy (main roads, secondary
roads...) that was symbolised by different hues is removed. Anyway this
information is unnecessary for trekkers.
