The Art and Science of Map Colour Scales
Maps are an incredibly powerful tool that allows us to visualize the world around us with greater clarity. They can display a vast array of information, ranging from the topography of mountain ranges to the intricate weather patterns in oceans. However, creating an accurate and effective map is a complex process that requires careful consideration of various factors, such as the colors used to represent different features.
Recent research has shed light on the intricacies of map reading, revealing that the way we interpret maps is a complex process that is influenced by a range of factors. As such, color selection is a crucial aspect of map creation, and choosing the right color scales for different types of maps can significantly improve their effectiveness. By gaining a better understanding of how maps are read and interpreted, we can create more accurate and informative maps that help us better understand the world around us.
The Mind Tricks Behind Map Reading
Maps are an invaluable resource that can give us a detailed understanding of the terrain and its various features. However, it’s important to keep in mind that our visual system has certain mechanisms that can potentially cause distortions in how we interpret maps. One such mechanism is known as simultaneous color contrast, which can have a significant impact on the way we perceive colors on a map. This phenomenon causes the color we see for a patch to appear darker on a light background than it would on a dark background. This can lead to inconsistencies in color perception and can make it challenging to accurately interpret the map’s colors and features.
This can be problematic for maps because nearby colors on the map can shift color values away from their true quantities, leading to substantial errors when reading metric values from maps. Researchers have tested this effect by having participants match map colors against keys, and the results have shown that careful scale design can minimize these perceptual quirks.
The Rainbow Myth
It is commonly believed that using a rainbow scale to show gradual quantitative changes on a map is the best approach. This is because the scale smoothly transitions through the entire visible color spectrum.
However, a recent study has found that the rainbow scale is prone to contrast-induced errors. Our visual system processes color information using opponent color channels that contrast red-green and blue-yellow. When color values change monotonically through one of these channels, such as in a rainbow scale, nearby colors can shift perceptions toward the opposite pole of that channel.
This means that using a rainbow scale, which moves through the red-green channel, can cause contrast effects that make it difficult to get accurate readings. This finding challenges the long-held belief that rainbow scales are visually optimal. Therefore, it is important to test our intuition rigorously.
Luminance Trumps Chroma
When we use maps, we rely on the colors and patterns of luminance to extract information and understand the details of the terrain. While colors help us identify the different regions, patterns of luminance, such as shadows, reveal the contours and textures of the surface, allowing us to perceive changes in the terrain shape.
Recently, a study was conducted to evaluate the effectiveness of different color scales in conveying aspects of surface shape, such as slopes and ridges. The study found that rainbow scales were not very useful in this regard, as our perception of shape-from-shading is more influenced by the luminance channels rather than color opponency.
Grayscale maps, however, are very effective in revealing shapes since the luminance channel is independent of the color channels. This means that grayscale maps are particularly good for showing the shape of the terrain, as they highlight subtle changes in the terrain’s features. However, grayscale maps cannot accurately convey quantities using different colors, which can pose a design challenge when trying to show the amount of a particular feature.
Best of Both Worlds
Researchers have developed an experimental color scale that can accurately show quantities and surface forms. This sequence changes chromatic hues while gradually increasing luminance values, resulting in a scale that conveys shape and minimizes errors when compared to other scales.
By utilizing different aspects of vision, such as luminance for shape and chroma for color matching, observers were able to extract both metric and form information accurately from this scale.
This research provides valuable insights into the complex perceptual mechanisms involved in map reading. With these principles, mapmakers can create optimized color scales that unlock the full potential of maps as invaluable visualization tools.
In summary, this experimental color scale reveals both terrain contours through luminance and quantitative changes using hue cycling. Rainbow scales led to the largest errors, while experimental scales minimized inaccuracy.
Note: This article is part of an assignment that requires me to summarize the paper “Color Sequences for Univariate Maps: Theory, Experiments, and Principles”
Reference: Color Sequences for Univariate Maps: Theory,
Experiments, and Principles, IEEE Computer Graphics and Applications, Sept 1988, 41–49, Colin Ware, University of New Brunswick, link
