Charlotte Hoarau

Reaching a Compromise between Contextual Constraints and Cartographic Rules: Application to Sustainable Maps

Emerging mobile mapping applications create new constraints for cartographers. These constraints should be considered in addition to the traditional cartographic rules used to design maps. Legend colors could be optimized regarding those constraints. A challenge for optimization concerns the preservation of map semiotic quality. In our research, we propose a quantification of the cartographic quality of a map, regarding a given reference map that considers semantic rules of association, differentiation and order conveyed by map colors. Some mobile devices require less energy to display dark colors than lighter ones. In this paper we consider the energy consumption as the contextual constraint to optimize. Map samples are designed, while taking into account some conventional uses of colors for relevant themes: hydrography, vegetation and the background layer. We discuss how to find the best compromise between a contextual constraint (the energy required to display a map on a screen of a mobile device in our example) and the cartographic consistency on colors regarding the initial semantic relationships in the legend. We answer the question of how much can cartographic rules be altered while still preserving semiotic quality.

Plan oblique relief for web maps

Plan oblique relief shows terrain with a side view on a two-dimensional map, resulting in visualizations where the third dimension of the terrain is more explicit than on traditional two-dimensional maps. Existing plan oblique maps are static: the angle of terrain inclination is not adjustable and the orientation of plan oblique inclination does not change with the orientation of the map. This article introduces two complementary methods that address these issues by using the 3D graphics pipeline to render plan oblique relief for tile-based web maps. The goal is to allow users to adjust the terrain inclination and map rotation angles to better visualize the third dimension of the terrain. The first method pre-renders plan oblique tiles with a server-side application. The tiles are visualized with a standard web mapping framework. The second method renders plan oblique relief on-the-fly in a web browser using WebGL and a customized version of OpenLayers 3, which enables users to select arbitrary terrain inclination and map rotation angles. The second method uses a tiled digital terrain model that is loaded by the web browser. The browser applies the plan oblique transformation, computes a shaded relief, and texturizes the terrain with tiled map layers.

Constrained palette-space exploration

Color palettes are widely used by artists to define colors of artworks and explore color designs. In general, artists select the colors of a palette by following a set of rules, e.g. contrast or relative luminance. Existing interactive palette exploration tools explore palette spaces following limited constraints defined as geometric configurations in color space e.g. harmony rules on the color wheel. Palette search algorithms sample palettes from color relations learned from an input dataset, however they cannot provide interactive user edits and palette refinement. We introduce in this work a new versatile formulation enabling the creation of constraint-based interactive palette exploration systems. Our technical contribution is a graph-based palette representation, from which we define palette exploration as a minimization problem that can be solved efficiently and provide real-time feedback. Based on our formulation, we introduce two interactive palette exploration strategies: constrained palette exploration, and for the first time, constrained palette interpolation. We demonstrate the performances of our approach on various application cases and evaluate how it helps users finding trade-offs between concurrent constraints.

Expressive Map Design Based on Pop Art: Revisit of Semiology of Graphics?

Is aesthetics an objective in the map design process? This question echoes our long-term research: does aesthetic quality improve map efficiency? In this paper, we discuss the notions of aesthetic response, objective and experience proposed by Kent (2005), and their relevance for making more expressive personalized maps. We first present the state of present research related to these notions and our interpretations. Then we present asystematic approach for rendering geographic data in a cartographic style based on the visual properties of Pop Art; the resulting maps are more vibrant and expressive. We consider this result a first step towards enhancing map quality. The proposition of a Pop Art cartographic style leads us to revisit some theoretical and practical principles of Semiology of Graphics (Bertin 1967), considering our experience with color contrasts and new approach for using texture. We conclude that expressive cartographic renderings would be useful for every mapmaker, and in the context of personalized map design, providing more elaborate tools could improve the design process and the resultant maps. Improving map quality is a question of managing visual variables in a traditional way—according to Bertin’s Semiology of Graphics —but also in a more artistic way, in order to find better cartographic representation according to the preferences, needs, and purposes of the mapmaker.