Interactive & Multiscale Thematic Maps: A Preliminary Study

Abstract

Problem: Interactive or "slippy" web maps have revolutionized cartography. Slippy maps present a single, coherentlydesigned reference map that can be panned to numerous geographic locations and zoomed across multiple scales. Further, they apply scale-dependent style rules to detailed geographic datasets, with the resulting designs rendered as a large set of interlocking tiles. To account for constraints in data bandwidth, processing, and storage, only those tiles relevant to the user's location and past interactions are served into the web browser or other application, resulting in a seamless, realtime user experience of "a map of everywhere". These slippy tilesets often are used as basemaps for advanced cartographic web and mobile applications, overlaying thematic information and other linework. Arguably, such slippy map mashups are the most common map seen and used today (and perhaps of all time). Yet, most of the cartographic design canon was developed long before slippy maps were possible. Do any of our time-tested design traditions in thematic cartography apply in today's interactive and multiscale mapping context? In this presentation, we discuss preliminary insights from an online map study about the design of interactive and multiscale thematic maps.Background: Our research integrates the cartographic tradition in thematic representation with growing research on interaction design. Thematic maps depict the distribution of one or several geographic phenomena, with the base reference information used as context for interpreting spatial variation in the thematic information [1]. Thematic maps grew in popularity in the 19 th century at the onset of the modern global economy as a method for tracking and controlling materials, labor, and goods [2], and, in today's information-driven society, are created by cartographers for reasons ranging from popular news reporting to exploratory scientific visualization. Thematic maps enable geographic imagination and spatial thinking, often representing abstract or statistical concepts that cannot be observed directly. Common thematic map types include choropleth, dot density, proportional symbol, and isoline, among others [3].Thematic maps can be organized in at least two ways. First, thematic map types differ in the visual variable used to encode the thematic information, or the basic graphic dimension separating variation in the thematic attribute of interest from other reference context [4]. For instance, choropleth maps typically employ the visual variables related to color (particularly color value, sometimes crossing multiple hues or saturations), dot density maps use a combination of arrangement and size, an emergent visual dimension sometimes described as "numerousness" [5], proportional symbol maps use size, and isoline maps use location (creating a new set of geographic linework based on thematic information), and also can include a color ramp between isolines similar to choropleth maps.Second, thematic maps differ in the visual metaphor they evoke in the relatio...

Do Different Map Types Support Map Reading Equally? Comparing Choropleth, Graduated Symbols, and Isoline Maps for Map Use Tasks

“…The group using the graduated symbols maps came second and the group using the isoline map had the worst results. Thus, the results obtained for non-interactive maps in this study were the opposite of those for interactive maps from the study by Roth et al [18,19] in which the isoline map guaranteed the highest accuracy. The differences in the results may be the effect of interactivity.…”

“…The highest number of statistically significant cases occurred for the task difficulty metric (in 7 tasks out of 11), and the least for the answer time metric (in 4 tasks out of 11). In contrast with studies comparing choropleth maps, dot maps, and graduated symbols by Mendonça and Delazari [30,31] and Roth et al [18,19], in which participants did not give better answers when using the choropleth map, yet they preferred it or assessed it as easy, in our study users of the choropleth map obtained the best performance metrics and assessed it as the easiest. Additionally, the results of the presented study are not coherent with the results of studies where there was no consistency in terms of performance metrics and subjective metrics [7,29].…”

“…Also when evaluating the choropleth maps, dot maps, and graduated symbols in the studies of Mendonça and Delazari [30,31], users preferred the choropleth map even though it turned out that they did not give better answers when using this map type. The same results for general tasks completed with choropleth were obtained by Roth et al [18,19].…”

“…This in turn provides support when selecting the most suitable map types in a given condition. For example, with regards to interactive maps, comparison of choropleth, dot density, proportional symbols, and isoline interactive maps, presenting the same data set at different scales, resulted in differences in the percentage of correct answers while completing elementary tasks [18,19]. The best results were obtained while using an isoline map, and the worst-a dot density map.…”

“…These kinds of characteristics are covered by many metrics: preference of choice [30,31], perceived level of difficulty [18,19,32,33], perceived level of confidence [18,19,34,35], rating of frustration/comfort when using a tested tool, and perceived speed of own performance [32].…”