Location, Color, and Form
Perception, Cognition, and Intuition
Location
The most elemental component of a geospatial story is location. Without knowing where something is, no visualization can be built. The accompanying image shows a data story using only the location of fire events. Naturally occurring fires tend to have an element of randomness to their geographic distribution, whereas these fires display a regular north-south alignment, and persistent clustering around particular locations. It is possible to infer simply from this spatial arrangement that these fires are likely to be anthropogenic in origin. A looping animation of these fires throughout the year of 2018 reveals that their location is remarkably stable, further evidence of a human created phenomenon. This particular distribution of fires comes from oil fields in Western Iran, and although satellite imagery could be brought to bear to explain this, it is a useful exercise as a designer to visually explain a concept with as little information as possible. In the case of a visualization designer working in the geospatial field, this minimum necessary information must be the location of a given phenomena.
Color
Color is an illustrative microcosm of the balance between art and science which a visualization designer must strike. The realities of human anatomy and perception bear heavily on selection of chromatic scales, and sufficient attention must be paid to the critical work of cartographic color researchers such as Cynthia Brewer. The science of determining what colors and differences are maximally perceptible to the human visual system is a complex branch of research which a visualization designer must study carefully and apply to any geospatial visualization they create in order to maximize legibility and clarity of storytelling. Not only must a chromatic scale be carefully chosen, but the function by which the scale is mapped to a given data set is of critical importance for communication. The accompanying image shows only one data set and one color scale, but the transfer function is different. In the case of quantized color application, the steps in color are mapped simply to the axis values of the data set. This leads to many color categories remaining empty and a visualization in which the single outlier hexbin in Iran is dramatically highlighted while the rest of the data is flattened. The quantile application of color applies each color category to a subset of the data itself, which guarantees that all color steps will have equal representation in the data. This produces an image in which there is greater visual difference between the subtle variations of the data set, however the extreme outlier blends into the rest of the image belying how truly different it is from the rest of the data. This example illustrates how critical the application of color is to geospatial data visualization, and how different a story can be told with the same data and color scale.
There is however, another side to this story. A scientifically based, appropriately mapped color scale can nonetheless be ineffectual in conveying the essence of a data set. A successful visualization designer must simultaneously choose colors which are dynamic, evocative, and maintain a close emotional connection to the meaning behind the data. In these visualizations, a dark basemap with colors that suggest fire helps to preserve the impact of the visualization and helps to communicate the power and danger of wildfire. The successful visualization designer must be able to apply both the art and the science of color to produce a truly effective image.
Form
Extending geospatial visualization into the third dimension adds significant complexity to the problems a designer must address. However it also offers opportunities to convey complex phenomena in powerful and effective ways. The accompanying image shows hexbinned wildfire data with hexpillar height representing the average plume height in the subregion, and hexpillar color representing the averaged radiative power in the subregion. Maintaining a close cognitive connection between visual variable expression and data property helps to clarify the image to the viewer by reducing cognitive load. Additionally, viewers can read multiple variables simultaneously in a manner which would be difficult to recapitulate in a two dimensional visualization.
