Observations and Reflections on Colour Palettes for Maps

Visualisation and personal preferences dominate the geoscientists favorite chosen colourbar. However, science can actually help us to guide our work, and we have put some thought into our choise of colour palettes for our regional structure maps to best represent the structures and avoid visually generating features that are not there.

Depth and thickness maps are represented by sequential data, and a reliable way to visualize sequential data is with a colour scale that continually increases or decreases a brightness ramp or a hue ramp.

This is shown in the example of the Perceived Lightness Graph for a perceptual palette, where you can see how the color lightness is perceived by the human eye closely correlates to a sequential dataset.

'Rainbow' or 'spectral' color palettes are not perceptual pallettes in the sense that the perceived values do not necessarily match the data variation. An interpreter should be aware that this color palette can introduce perceived thresholds and contrasts in the map where non exists in the data. It should also be noted that this palette can reduce the emphasis on details that are present in the underling data. Most of the issue with this palette is due to the use of bright colors (yellow, green and cyan) on non-extreme positions of the scale, this introduces perceived sharp transitions as shown in the example with the Perceived Lightness Graph for the ‘Rainbow’ Palette.

The default time or depth 'rainbow' palettes used by DUG InsightTM is used in our daily work . For final depth maps in reports, a modified version of 'rainbow' palette is used where the red and yellow colors have been switched positions on the scale. This minimizes to some extent the issues and limitations described on the above paragraph.

A simple comparison of both colour palette used is shown in the example.