Module 4 of Communicating GIS took students on a journey of color. This week we learned the extent at which color impacts a map and the information being communicated. We have had to take into consideration which colors usually or best represent specific types of data, how the human eyes interpret color, how colors interact with each other, and the ways color can vary in hue, saturation and lightness of value. While we focused on the RGB and HSV color systems, we also explored displaying quantitative data and using color ramps to symbolize sequential and divergent data.
The following images show three color ramps. All of the color ramps were created using the RGB color system, however, each was created utilizing a different method. The first ramp was created by choosing the darkest and lightest hues, followed by determining the 4 shades in between at an equal interval. The second ramp utilized the same darkest and lightest hue, but the 4 shades in between were determines using intervals with an adjusted progression, with the interval nearest the darkest hue having a larger interval and the interval nearer the lightest hue having a smaller interval. The last color ramp was created using a sited called Color Brewer which can easily create the ramp for you, based on the options you choose.
Color Ramp 1: Equal Intervals
Color Ramp 2: Adjusted Progression Intervals
Color Ramp 3: Color Brewer Produced
While all of the color ramps can be used, the two manually created ramps have less variation in lightness and saturation, which could be less appropriate for some maps. It is also worth noting that the Adjusted progression color ramp has a less noticeable change in lightness in the lighter colors (for this particular color scheme), which can also be problematic.
The map below also highlights the use of color to communicate information. This particular map is a Choropleth map of Georgia, showing population change, by county, in Georgia between 2010 and 2014.
For this map I chose the natural breaks method using nine classes. The choice to have nine classes was to ensure that the map reader could clearly see the progression of percent change in, both, the positive and negative direction. The mid-point of the classes is symbolized with a neutral light color that is close to white. It lacks a hue of any significance, which can be associated with little or no change. The values of positive change are symbolized in various shades of green with the lightest green showing a small increase and the darkest, most saturated green showing the largest increase. The values of negative change are symbolized in various shades of purple with the lightest purple showing a small decrease and the darkest, most saturated purple showing the largest decrease. I also chose shades of green and purple because they generally do not have a negative association and are not affiliated with any specific groups.
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