Dot distribution map

Abstract: Interview findings suggest perceived proximity to mapped hazards influences risk beliefs when people view environmental hazard maps. For dot maps, four attributes of mapped hazards influenced beliefs: hazard value, proximity, prevalence, and dot patterns. In order to quantify the collective influence of these attributes for viewers' perceived or actual map locations, we present a model to estimate proximity-based hazard or risk (PBH) and share study results that indicate how modeled PBH and map attributes influenced risk beliefs. The randomized survey study among 447 university students assessed risk beliefs for 24 dot maps that systematically varied by the four attributes. Maps depicted water test results for a fictitious hazardous substance in private residential wells and included a designated "you live here" location. Of the nine variables that assessed risk beliefs, the numerical susceptibility variable was most consistently and strongly related to map attributes and PBH. Hazard value, location in or out of a clustered dot pattern, and distance had the largest effects on susceptibility. Sometimes, hazard value interacted with other attributes, for example, distance had stronger effects on susceptibility for larger than smaller hazard values. For all combined maps, PBH explained about the same amount of variance in susceptibility as did attributes. Modeled PBH may have utility for studying the influence of proximity to mapped hazards on risk beliefs, protective behavior, and other dependent variables. Further work is needed to examine these influences for more realistic maps and representative study samples.

Abstract: Geographical mapping of infectious diseases is an important tool for detecting and characterising outbreaks. Two common mapping methods, dot maps and incidence maps, have important shortcomings. The former does not represent population density and can compromise case privacy, and the latter relies on pre-defined administrative boundaries. We propose a method that overcomes these limitations: dot map cartograms. These create a point pattern of cases while reshaping spatial units, such that spatial area becomes proportional to population size. We compared these dot map cartograms with standard dot maps and incidence maps on four criteria, using two example datasets. Dot map cartograms were able to illustrate both incidence and absolute numbers of cases (criterion 1): they revealed potential source locations (Q fever, the Netherlands) and clusters with high incidence (pertussis, Germany). Unlike incidence maps, they were insensitive to choices regarding spatial scale (criterion 2). Dot map cartograms ensured the privacy of cases (criterion 3) by spatial distortion; however, this occurred at the expense of recognition of locations (criterion 4). We demonstrate that dot map cartograms are a valuable method for detection and visualisation of infectious disease outbreaks, which facilitates informed and appropriate actions by public health professionals, to investigate and control outbreaks.

Abstract: Methods of portraying multiple distributions in the same map space are limited to a few, largely untested symbolization techniques. This paper investigates one of those techniques, the multi-pattern color dot map. A perception test is employed comparing the relative effectiveness of the multi-pattern map to single distribution dot maps in conveying'regional distribution information to map readers. Responses are analyzed with two measures: the consistency with which subjects defined region boundaries within the map; and the internal accuracy of regions identified. Results suggest that color dot maps are at least as effective as several single black and white dot maps in portraying regions. Les methodes pour produire une carte montrant la repartition de plusieurs phenomenes se resument a quelques techniques semiologiques peu verifiees. Cet article etudie une de ces techniques, la carte en couleurs par points a phenomenes multiples. On verifie a l'aide d'un test de perception l'efficacite des cartes a phenom...

Abstract: This paper analyzes the perception of spatial dispersion on point distributions. Spatial dispersion is one of the major concepts communicated by dot maps. To promote efficient communication of this concept, two experiments were conducted to investigate the relationship between the perception of spatial dispersion and such map characteristics as spatial arrangement of points, number of points, symbol size, and map scale. Regression models were built on the basis of the experimental results to describe the relationship quantitatively. The obtained models enable map authors to predict the degree of spatial dispersion perceived by map readers. From the models and the results of a computer-assisted simulation, the following conclusions were obtained: 1) map scale greatly affects the perception of spatial dispersion; 2) spatial arrangement of points and number of points are also influential; 3) the size of point symbols does not significantly affect the perception of spatial dispersion.