GEOM90007 Chap.5 Colour, Light and Accessible Scales

Colour, Light and Accessible Scales

Define colour channel

Colour, Light and Accessible Scales connects colour channel, sequential colour scale and colour accessibility along an information-visualisation pipeline: data type, visual encoding, perception, task fit and evaluation.

The practical aim is to select a categorical, sequential or diverging scale from the data semantics and test it without colour alone; the display is defensible only when each encoding choice can be traced back to the analytical question and the structure of the data.

Place colour channel at its correct stage: question, data specification, transformation, encoding, perception, tool or evaluation.

For colour channel, record the variables, measurement levels, granularity, missingness and comparison task wherever they apply before choosing or judging a chart.

Use sequential colour scale to make the next transformation, encoding, layout, interaction or evaluation step explicit.

When sequential colour scale involves marks and channels, state which values they represent and check whether scale, ordering, aggregation or filtering changes the apparent pattern.

Use colour accessibility to test perceptual and task fit.

In Colour, Light and Accessible Scales, ask whether viewers can make the required comparison accurately, whether uncertainty and exceptions remain visible, and whether colour, position, motion or interaction creates an avoidable accessibility or interpretation cost.

Trace sequential colour scale

For the application — select a categorical, sequential or diverging scale from the data semantics and test it without colour alone — compare at least one alternative encoding against the same data and task.

Retain the design only if the colour accessibility evaluation shows that it reveals the intended relationship without introducing a stronger distortion or hiding the evidence needed to challenge it.

Make a compact pipeline audit for colour channel: question or data field; transformation; mark and visual channel where applicable; intended task; evaluation evidence; and likely failure.

Locate sequential colour scale and colour accessibility at their actual stages so a technically valid implementation is not mistaken for an effective display.

Test a changed sequential colour scale view. Hold the data and question stable, replace the channel most closely tied to sequential colour scale, and predict which comparison becomes easier or harder.

Evaluate the result with colour accessibility, including uncertainty, accessibility and the possibility that an apparent pattern is produced by scale, binning, projection or interaction state.

Critique Colour, Light and Accessible Scales in task order: state the question around colour channel, classify the data, describe the role of sequential colour scale, predict the perceptual judgement and report the colour accessibility evaluation evidence.

Revise the first stage where colour accessibility shows that the visual no longer supports the task instead of adding decoration to a structurally unsuitable chart.

Test with colour accessibility

A complete response should make the task visible before the detail: identify what must be decided, define the relevant terms, connect the evidence to sequential colour scale, and use colour accessibility to test the result.

The final sentence about colour accessibility should answer the question actually asked rather than merely repeat the topic.

The controlling limit is specific: Rainbow-like variation can create false boundaries and colour should not be the only carrier of critical meaning.

Keep that colour accessibility limit beside the worked example, because it separates a careful GEOM90007 answer from one that sounds confident but claims more than the task or evidence supports.

For revision, retrieve colour channel, sequential colour scale and colour accessibility without notes, explain their relationship aloud, then complete a changed version of the application: select a categorical, sequential or diverging scale from the data semantics and test it without colour alone.

Record the first failed sequential colour scale reasoning move and repair it before attempting another case.

What this chapter covers

• 01

  colour channel

• 02

  sequential colour scale

• 03

  colour accessibility

• 04

  Applying colour channel

• 05

  Limits of sequential colour scale and colour accessibility

Worked example: Colour, Light and Accessible Scales

Key terms

colour channel

A visual encoding using hue, lightness or saturation to represent categories, order, magnitude or emphasis. Use this definition when the task is to select a categorical, sequential or diverging scale from the data semantics and test it without colour alone.

sequential colour scale

An ordered progression in lightness or saturation used to represent values increasing from low to high. Use this definition when the task is to select a categorical, sequential or diverging scale from the data semantics and test it without colour alone.

colour accessibility

The design of colour encodings so distinctions remain perceivable under varied vision, displays, print and viewing conditions. Use this definition when the task is to select a categorical, sequential or diverging scale from the data semantics and test it without colour alone.

Colour, Light and Accessible Scales FAQ

Assessment move

Reconstruct the relationship among colour channel, sequential colour scale and colour accessibility; complete the chapter application without notes; then test the result against this limit: Rainbow-like variation can create false boundaries and colour should not be the only carrier of critical meaning.

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