Highlighting in Geovisualization

Coordinated view geovisualizations allow users to interactively pick and attend to data observations across multiple views. This is frequently supported by the transient application of a visual effect to an observation during a mouse selection or rollover. This technique, known as highlighting, is typically implemented using a dedicated bright and saturated color to outline observations. In this paper we present a range of possibilities for alternative approaches to color highlighting, beginning with examples from the range of available visual variables and moving beyond those options to other, non-visual variable methods such as the use of lines to connect highlighted observations. We also describe design criteria for highlighting methods that can be used to predict and test the suitability of different approaches, and apply those criteria to our set of proposed methods to identify potential good candidates for implementation in future systems. Next, we present a set of highlighting types that define basic ways in which highlighting methods can be combined, modified, and driven directly by data values. We conclude by outlining several broad research challenges for future work on the development and evaluation of highlighting methods in geographic visualization.     

Exploration of Information Theoretic Arguments for the Limited Amount of Information in a Map

From the application of information theory capacity limits of maps are derived and some cartographic rules are formulated—based on theoretical models and perception studies. The perception study shows that for a relief map with coloured height intervals the channel capacity, as defined in information theory, is reached at seven～eight height classes. Generally, the length of a visual variable may be characterized by the channel capacity of the map. This theoretical study shows how increased attention should be paid to perceptual separation as the number of categories increases. The requirement becomes more and more crucial as the number of categories exceeds five. The principle of group visibility is formulated and demonstrated. Group visibility considers the visibility of groups of map features and may be utilized in a visual search for geographical patterns. The quantitative measures presented offers computational methods to control group visibility for example in an interactive visualization system.