Reaching a Compromise between Contextual Constraints and Cartographic Rules: Application to Sustainable Maps
Hoarau, Charlotte, Cartography and Geographic Information Science
The ever-increasing demand for mapping, as well as the need for different kinds of maps and mapping products has accelerated the development of more diverse mapping applications. Cartographers and map designers have responded to these increasingly diverse needs by developing maps that are responsive to different visualization contexts and to individual user needs. In order to create these new visualizations, it is often useful to add some constraints to the traditional cartographic rules. For example, depending on the context, maps might sometimes be less complex, less luminous or maybe limit the use of color. Cartographers should consider these constraints in order to design the most suitable map for any given context keeping in mind that for a map to 'make sense', the chosen symbolization must be consistent with the semantic relationships it represents.
This article explores the extent to which a given topographic map can be modified according to a given constraint without loosing the meaning of the initial map. An evaluation of the semiotic quality of a modified map to an initial reference map is presented. This evaluation quantifies the semantic relationships of association, differentiation and order in the initial map, and measures how well the final map conveys these semantic relations.
The method employed in this study is based on map designs that have been created with decreasing adherence to cartographic guidelines so as to adapt a map for display on a mobile device. A practical constraint was to lower the energy required to display a map by redesigning the legend and modifying the colors. These energy savings are useful, for example to trekkers to increase the battery life of their GPS, or any other mobile user of GPS.
This article begins with a discussion of estimation of semiotic quality, and the energy required to display a map on a mobile device. The four map samples are compared to determine the relative compromises between traditional cartographic guidelines and the contextual constraint of reducing energy use for the display of maps on mobile devices.
Semiotic Quality of a Map
Cartographic theory provides a detailed formalization of graphical semiotics. Bertin (1967), as described in MacEachren (1995) presents different graphical variables and the correct ways to use them during cartographic conception. In this study the following two of Bertin's cartographic rules are considered: (1) conventional color uses, called conventional rules in this paper, and (2) semantic rules, that structure the organization of the legend by semantic relationships of association, differentiation and order.
Conventional rules limit the color space for some themes, as illustrated in Figure 1. In this example convention suggests that hydrography be represented by a color of the blue family, vegetation by a color of the green family and the background layer by a light color. Conventional rules facilitate the understanding of maps because people are often familiar with the conventions. Of course, it is possible to represent forest by red (which is sometimes relevant in fall) but this is not typical.
[FIGURE 1 OMITTED]
As illustrated in Figure 2, semantic rules link two themes and their color. Two themes involved in an association relationship should be represented by similar colors, whereas two themes involved in a differential relationship should be represented by distant colors. Finally, themes involved in an ordered relationship should be represented by a color shading of the same hue.
In the legend, color choices play a major role because they are supposed to convey the existing semantic relationships between their corresponding themes. They ensure the semiotic quality of the map. For example, ColorBrewer (Brewer 2003) provides color schemas adapted to thematic cartography. Christophe (2009) proposes a cooperative method to design customized and original legends, by helping users to select suitable colors. …