What is the best color ramp for topographic data?

Recent work from Megan Henriksen and the LROC team is improving their color-shaded relief and slope maps, see New Dynamically Generated Color-shaded Reliefs For Narrow Angle Camera Digital Terrain Models.

@thare pointed out that although it’s a major step away from the traditional rainbow color ramp (see NASA please no rainbows, troubles with rainbows or a dangerous rainbow), we can question the use of divergent color ramps for topography, especially for people with Color Vision Deficiency (CVD).

  • Quote: “A divergent colormap is used to compare data values to a reference value in a way that visually highlights whether values are above or below the reference.” [ref].
  • Topography generally doesn’t have that reference (even including sea-level for Earth).


We propose to produce and test different color ramps, including:

References:

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Just to expand on Trent’s point about divergent color ramps and topography:

The issue is not so much that divergent color ramps are intrinsically bad for people with CVD. There are several CVD-safe divergent ramps available. Divergent color ramps are just more appropriate when the intention is to draw attention to divergence from some critical value. The classic application for divergent ramps is temperature difference maps: Use a Red-Blue color ramp with white in the middle to show positive (usually blue) and negative (usually red) deviations from an average value (white).

For topography, it is more appropriate to use a color ramp whose apparent lightness changes monotonically and (with a few exceptions) linearly.

I encourage folks to read Rob Simmon’s 6-part series “Subtleties of Color” to gain a better understanding of basic color theory and how to apply it to geospatial data. Part 1 is available here:
https://earthobservatory.nasa.gov/blogs/elegantfigures/2013/08/05/subtleties-of-color-part-1-of-6/

also useful --> https://mycarta.wordpress.com/color-palettes/ (and links/posts therein)

Here is a color blindless simulator

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Maybe useful : https://personal.sron.nl/~pault/

From the website Introduction:

"
It is convenient to have good default schemes ready for each type of data, with colours that are:

** distinct for all people, including colour-blind readers;*
** distinct from black and white;*
** distinct on screen and paper;*
** matching well together.*

This site shows such schemes, developed with the help of mathematical descriptions of colour differences and the two main types of colour-blind vision. A colour scheme should reflect the type of data shown. There are three basic types of data:

** [Qualitative data] – nominal or categorical data, where magnitude differences are not relevant. This includes lines in plots and text in presentations.*
** [Diverging data] – data ordered between two extremes where the midpoint is important, e.g. positive and negative deviations from zero or a mean.*
** [Sequential data] – data ordered from low to high.*
"

Matplotlib has done a good review of their colors for version 2, and there is some nice material – also about customizing palette --, here are some references to the discussion: