Difference of Perceptual Tasks in Cleveland and McGill’s elementary

ELEMENTARY PERCEPTUAL TASKS AND VISUAL VARIABLES
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How Cleveland and McGill’s elementary perceptual tasks differ from Bertin’s proposed visual variables.
Perception is the capacity of viewers to interpret visual encodings of quantitative and qualitative information in graphs. Graphical perception can be described also as the ability to recognize the visual encoding of information. Visual variables are the graphic dimensions across which a map or other visualizations can be varied to encode information. Elementary Perceptual Tasks are the basic visual building blocks used to compare quantities.
Jacques Bertin was the first French cartographer to develop the idea of visual variables. He identified seven classes of visual variables which were; position, size, shape, value, color, orientation, and texture. McGill’s elementary perceptual tasks directly elucidate Bertin’s two variables which are the position and color variables. Cleveland’s length, area, and, the volume can be translated as the size and shape viewpoint. Bertin’s color can be related to McGill’s shading and color saturation, whereby color saturation is the least in order of perceptual tasks.
Bertin also captures value, orientation, and texture. Value in terms of how light or dark an object looks in a map can be correlated to McGill’s saturation task as chiefly employed in heat maps or choropleth maps. Bertin’s orientation can compare directly to McGill’s angle and the direction labels and symbols are pointing to on pie or bar charts. Finally, Texture as noted in Bertin’s concept can be translated to Cleveland's and McGill’s shading. Here, the dense network of lines denotes certain areas in a map. Curvature is the variable that cannot be associated with Bertin’s visual variable Model. Curvature entails the dimension a bar chart is portrayed; either being 3D, 2D, or 1D.
Primary and secondary perceptual tasks proposed on the map of Murder rates in 1978
Primary perceptual tasks on this map are the shading and square sizes. We suppose that by different linear spacing and degrees of shading, we can distinguish the primary task used to derive data. A secondary task interprets the area of the shaded parts. From this map, the primary perception is that murder rates were registered everywhere in the US during the year 1978. The secondary perception indicates that the degree differs as the magnitude of the problem hit majorly towards the southern states. One can understand that the southern states in the US were inhabitable in that year. The areas covered by the darkest shades indicate fatal levels while the lighter shades from lines indicate a lesser prevalence of the problem. Without critically examining the key, the secondary perception from the map is that the crime rates in a majority of the states are high. The darkest of them induces the idea that one cannot conveniently live in those states. On the other hand, the larger squares are a visual depiction of safety. From the graphical representation, one can infer that the US was a very unsafe place to reside in through the year 1978.
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Cleveland and McGill...