CARTO: The Map Academy (How to Choose Map Colors) - A Summary

Written by TJ Hutchisson

The CARTO website offers The Map Academy, a set of free tutorials/exercises ranging from easy to hard to mixed, focusing on topics such as map design, working with data tables to create interactive maps, or how to use CARTO’s JavaScript library. The proclaimed goal of The Map Academy is for users to “learn to create maps on the web and visualize geospatial data.” This summary focuses on a section titled Intermediate Map Design, and more specifically How To Choose Map Colors, Part 1.
 
How to Choose Map Colors is split into two parts: Part 1 discussing color perception, and Part 2 on choosing proper schemes. The topics covered in this first lesson are a mixture of general color theory, and how to specify color in CARTO. The lesson very briefly introduces the color spectrum and the concept of color relationships, providing examples of complementary and analogous colors. 

The lesson then addresses how to adjust for legibility using hue, saturation, and value. These terms are BRIEFLY defined, and no hard and fast rules are given about how exactly to change these qualities in the most effective manner. This section seems intentionally vague, asking the viewer to use their judgment, and ultimately provides outside resources for when your colors are not working well together. However, an effective example is used to demonstrate how altering saturation and brightness can dramatically change the perception. 

The high contrast makes these colors nearly vibrate. 

These toned down colors are much easier on the eyes.
 
The lesson then becomes geared specifically to CARTO, and the numerous ways in which you can define color in CartoCSS.

• HTML color names
• Hexadecimal code
• RGB (Red Green Blue)
• RGBA (plus color transparency)
• HSL (Hue Saturation Lightness)
• HSLA (plus color transparency)

 
The lesson ends with other considerations when selecting and adjusting colors. First and foremost, considering the accessibility of maps, particularly for people with color blindness and limited vision. Again, outside resources are offered for checking this aspect of legibility.

​Other considerations mentioned:

• Simultaneous Contrast - when there is a perceived color shift due to the colors it is seen against

• Contrast of Extension - the harshness of contrast due the proportion of the color areas
  
• Rainbow Palettes - the tendency to perceive features that are not actually there

 
Overall, this lesson is only a cursory look at color and color perception. While none of the topics or terms are defined in depth, this section of the Map Academy does serve as a good starting point, and ultimately is more useful as a tool for providing a list of resources.