Using Flow Maps to Visualize Time-Series Data: Comparing the Effectiveness of a Paper Map Series, a Computer Map Series, and Animation

Motion and change through time are important aspects of thematic maps. Traditionally, such data have been visualized using a series of paper maps that represent multiple snapshots of a location over time. These maps are visually compared by the map reader when analyzing change over time for a location. This static view of change over time has worked well for cartographers in the past, but today computer animation allows cartographers to emphasize the dynamic nature of this data. By animating a map, change over time can be represented on one map rather than in a traditional map series. This study compared a paper map series, a computer map series, and animated maps of the same data to assess the effectiveness of each technique for memorizing data symbolized by graduated flow lines. Subjects were asked to study the maps and to memorize two types of information: quantity data at specified locations on the maps and trend patterns that occurred over the maps. Memorization of the information was subsequently tested using a series of multiple choice questions. Analysis of response times and accuracy rates for these questions suggest that animation does not improve learning ability for quantity evaluations. It does appear, however, to improve subjects' abilities to learn and remember trend patterns in the data. Results also indicate gender differences in using animated maps

Visual Search Processes and the Multivariate Point Symbol

This study reviews the major theories of visual search processes and applies some of their concepts to searching for multivariate point symbols in a map environment. The act of searching a map for information is a primary activity undertaken during map-reading. The complexity of this process will vary, of course, with symbol design and map content. Multivariate symbols, for example, will be more difficult to search for efficiently than univariate symbols. The purpose of this research was to examine the cognitive processes used by map readers when searching for multivariate point symbols on a map. The experiment used Chernoff Faces as the test symbol, and a symbol-detection task to assess how accurately and how efficiently target symbols composed of different combinations of facial features could be detected. Of particular interest was assessing the role that different combinations of symbol dimensions and different combinations of symbol parts played in moderating search efficiency. Subject reaction times and error rates were used to evaluate the efficiency of the searches. Results suggested all searches employed serial search processes, although feature searches (those in which a target symbol consists of a unique feature) were by far the easiest for subjects to complete. It was also demonstrated that hierarchical relationships could be manipulated within symbols to increase search efficiency for searches in which the target does not have a unique feature (conjunctive search)

Males, Females, and Maps: Evaluating Spatial Encoding Strategies

Cognitive research suggests that there is a difference in the spatial abilities of males and females. Results of studies that examine way-finding skills indicate that the differences found may be linked to a variation in the types of strategies used in completing spatial tasks. The purpose of this study was to assess the influence of gender on different strategies for encoding spatial information in a map context. An experiment was conducted in which subjects studied a map presented to them using one of three encoding strategies: (1) a control strategy in which they viewed the map as a static representation, (2) a landmark-based strategy in which they viewed a dynamic sequencing of the map that began with landmark locations and built over time to include all map components, and (3) a path-based strategy in which they viewed a dynamic sequencing of the map that began with path locations and built over time to include all map components. Following this study phase, subjects completed a series of map recognition tasks where they indicated whether a presented map was the same as or different from the map they had originally studied. Test maps that differed from the memorized map were modified by either replacing, displacing, or reversing the perspective of a map object. Results indicated that while encoding strategy played a significant role in determining how accurately subjects could perform the recognition task, gender did not significantly influence how well any particular strategy worked for encoding map-based spatial information

The Face Symbol: Research Issues and Cartographic Potential

The face symbol, developed by Herman Chernoff (1973), is possibly the seminal multivariate point symbol. Cartographically, the symbol has made an appearance several times, but it has often been criticized because designers tend to ignore two key symbol parameters: feature salience and natural correspondence. Feature salience is the concept of perceptually ordering facial features from those that produce the most noticeable changes to those that produce the least noticeable changes. Natural correspondence refers to designing face symbols so that the overall attitudinal labels of the symbols correspond to the overall physical meaning of the mapped data. It is argued here that feature salience and natural correspondence may be treated as special cases of visual attention in relation to symbol design. From this perspective, these symbols deserve a new look cartographically. This research reports on symbol variations, explores feature salience and natural correspondence, addresses user environments and tasks, and speculates on future experimental designs that may lead to more effective map use of this symbol

Choropleth Maps on High Resolution CRTs: The Effects of Number of Classes and Hue on Communication.

The research reported here was designed to determine how quickly and accurately map readers viewing choropleth maps on a high-resolution computer monitor are able to identify to which class an areal unit on the map belongs, when the map has between four and eight classes and is produced in shades of either gray, green or magenta. As expected, accuracy rates decreased and reaction times increased as the number of classes on the map increased, Accuracy rates ranged from 91.9% for four-class maps to 68.2% for eight-class maps (averaged for all three colors used in the study). Hue also affected accuracy rates and reaction times, the best results being obtained with achromatic (gray-shaded) maps: 84.5% correct, averaged over all numbers of classes. Maps shaded with magenta proved to be the least satisfactory with an accuracy rate of 72.8%. The study provides cartographers with empirical guidelines regarding what level of map-reading accuracy might be expected for choropleth maps designed with a given number of map classes, in a specific hue, and displayed on a high-resolution graphics monitor

Designing Effective Bivariate Symbols: The Influence of Perceptual Grouping Processes

The purpose of this research was to empirically assess perceptual groupings of various combinations of symbol dimensions (e.g., graphic variables) used in designing bivariate map symbols. Perceptual grouping ability was assessed using the theory of selective attention, a construct first proposed in psychological research. Selective attention theory contends that one's ability to analyze a symbol's dimensions—such as color or size—is affected by other dimensions present in the same symbol. Symbol dimensions are described as either separable (capable of being attended to independently of other dimensions), integral (cannot be processed without interference from other dimensions), or configural (i.e., show characteristics of both integrality and separability, which may also form new, emergent properties). Without empirical evidence describing such interactions for various combinations of symbol dimensions, cartographers cannot truly evaluate the functionality of the symbols they use on maps. The symbol dimensions or graphic combinations chosen for this study were selected to incorporate a wide range of traditional cartographic symbolization, including line and lettering symbolization, areal shading, dot patterns, and point symbols. Combinations were examined in an abstract setting using a speeded classification task, which is the traditional means of studying selective attention. Subject reaction times provided an assessment of the levels of integrality, separability, and configurality. Results suggest that most symbol dimension combinations are either separable or exhibit evidence of asymmetrical dimensional interactions. Findings from this study will be integrated into subsequent experiments, the results of which will assist cartographers in the design of complex map symbols

Colour Detection on Bivariate Choropleth Maps: The Visual Search Process

Searching is a fundamental but complex task in the map-reading process. Several psychologists have explored the role of visual search in cognition, and have proposed a number of models that may offer cartographers a basis for understanding how people search for specific map information. The purpose of this research was to examine the visual search process used by map readers when interacting with bivariate choropleth maps, and to assess the potential of one of psychology's models, Attentional Engagement Theory, for explaining that process. The study employed a standard search task that determined the efficiency of the search process by having subjects search for target colours among non-target colours across a map. An analysis of reaction times showed that the following variables affected search efficiency: target colour, the total number of objects on the map, and similarity of the target colour to all other non-target colours on the map

Amending the North Carolina Constitution: Spatial and Political Enfranchisement as Portrayed By Delegate Votes and Voter Representation in 1835

The most significant event in the political history of antebellum North Carolina was the convention that assembled at Raleigh on 4 June 1835 to amend the North Carolina Constitution. At that time, it had become apparent that the North Carolina Constitution of 1776 was seriously flawed. When the convention was adjourned on 11 June 1835, the delegates had prepared amendments that abolished borough representation, secured better representation for the western counties, allowed for election of the governor by the people rather than the Legislature, and removed certain religious qualifications for holding office. Unfortunately, they also submitted an abrogation the right of free persons of color to vote. When the amendments were submitted to the citizens of the state for ratification, the tabulation of popular vote reflected a stark contrast between the counties of the east, favoring rejection of the amendments, and the counties of the Piedmont and Mountains that supported their ratification. With such a solid division between the regions, it is difficult to determine county-level sentiment on any particular amendment. The votes of the delegates to the convention, however, were not always so clearly divided along sectional lines when they were crafting the amendments. By mapping the spatial distribution of the votes of the delegates on the individual amendments, county-level attributes of the popular vote emerge

Visualizing Data Certainty: A Case Study Using Graduated Circle Maps

Several techniques have been proposed for displaying data certainty on maps, but few have been empirically tested for effectiveness. While it is important to make data certainty information easily accessible, the addition of such data should not unduly increase map complexity. Thus, it becomes important for cartographers to examine the available methods for displaying this aspect of metadata and to test each for its effectiveness. The focus of this study was the display of data certainty information on graduated circle maps. Four types of accuracy indicators were evaluated for their effectiveness in communicating data certainty information. Two were traditional accuracy indicators: reliability diagrams and legend statements. Two were bivariate in form, one using a value-size combination and the other mimicking the idea of focus by varying the line value of the graduated circles to suggest a fading of symbolization for least certain data. The study was designed to assess whether subjects could identify data certainty information on test maps, and evaluate how accurately and confidently they could extract and interpret both thematic and data certainty information. Mean accuracy and confidence rates were compared for maps using different accuracy indicators to evaluate their relative effectiveness. Results suggest that subjects had most difficulty identifying and extracting data certainty information using maps that employed legend statements. They were most successful when data certainty was wedded to thematic data on the map using the bivariate accuracy indicator that mimicked the concept of focus. Identification and extraction of thematic data values were not significantly affected by choice of accuracy indicator

A review of How Maps Work: Representation, Visualization, and Design by Alan M. MacEachren.

If you are searching for a detailed guide to contemporary cartographic research issues, How Maps Work is the book you need. This encyclopedia volume covers many of the major ideas currently being examined by academic cartographers. The goal of the book, as stated by MacEachren, is to provide a basis from which cartographers might begin to build an understanding of how maps work. As he clearly points out in the preface “Understanding how and why maps work (or do not work) as representations in their own right and as prompts to further representations, and what it means for a map to work, are critical issues as we embark on a visual information age” (p. v)