Estimated reading time: 2 minutes

Summary

Colour can play a major role in the visualisation of data, as can an absence of colour.
Returning to the scale of explanatory and exploratory visualisations can help us think about how colour can help communicate research data.

In visual communication, colour is a powerful conveyor of information, and colours of different hues, values and saturations can play a major role in the visualisation of data. The same applies to the absence of colour, whether or not that absence was preceded by a conscious choice.

According to Mackinlay's ranking of processes related to perception, colour is one of many ways with which we encode information. As with the majority of encoding methods, its effectiveness varies depending on the data. Mackinlay's system suggests that colour is best used to encode nominal data, that is, category data that cannot be ranked. In addition, colour can be used to emphasize or distinguish one graphic element from another. However, colour tends to work less well for coding quantitative data, i.e. for expressing quantity or frequency. A clear exception is when colour is the primary conveyor of information, as is the case with colour charts and choropleth maps.

To demonstrate this, let's return to the principles of explanatory and exploratory visualisation mentioned in the introductory module on visualisation.

Explanatory use of colour

In the example below, colour has been used for explanatory purposes. Here, it distinguishes different continents from each other. The countries' population is described by area. In the x and y axes, child mortality and food security are expressed by position.

Diagram över livsmedelsförsörjning/barnadödlighet där färgkodning används.

Source: Free material from www.gapminder.org. Creative Commons BY

Exploratory use of colour

In a more exploratory example of visualisation, colour is nonetheless applied in the same way: to distinguish one graphical element from another.

In the diagram below (an echocardiographic image using colour Doppler to visualise the velocity and direction of blood flow), colour has been used to separate different components from each other.

Ultraljudsbild av hjärtat där doppler använts för att visualisera flödeshastighet och flödesriktning.

An echocardiographic image using color Doppler to visualize the velocity and direction of blood flow.

Source: Wikimedia Commons. Public domain.

For instance, colour is used to visualise the direction of blood flow: blue indicates flow direction away from the transmitter, red indicates direction towards the transmitter. Variations in value then describe flow velocity: the lighter the color, the higher the velocity. Area, meanwhile, represents volume.

Explanation of terms

Colour is the specified colour, such as red, yellow or green.
Value is the lightness of the specified colour, such as light green or dark green.
Saturation describes the clarity of the specified colour and how close the colour is to a grey of the same value.