GEOM90007 Chap.7 Chart Selection, Comparison and Uncertainty

Chart Selection, Comparison and Uncertainty

Define analytical task

Chart Selection, Comparison and Uncertainty connects analytical task, chart grammar and uncertainty representation along an information-visualisation pipeline: data type, visual encoding, perception, task fit and evaluation.

The practical aim is to choose a chart from the task and data structure, then make uncertainty commensurate with the claim; the display is defensible only when each encoding choice can be traced back to the analytical question and the structure of the data.

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

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

Use chart grammar to make the next transformation, encoding, layout, interaction or evaluation step explicit.

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

Use uncertainty representation to test perceptual and task fit.

In Chart Selection, Comparison and Uncertainty, 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 chart grammar

For the application — choose a chart from the task and data structure, then make uncertainty commensurate with the claim — compare at least one alternative encoding against the same data and task.

Retain the design only if the uncertainty representation 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 analytical task: question or data field; transformation; mark and visual channel where applicable; intended task; evaluation evidence; and likely failure.

Locate chart grammar and uncertainty representation at their actual stages so a technically valid implementation is not mistaken for an effective display.

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

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

Critique Chart Selection, Comparison and Uncertainty in task order: state the question around analytical task, classify the data, describe the role of chart grammar, predict the perceptual judgement and report the uncertainty representation evaluation evidence.

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

Test with uncertainty representation

A complete response should make the task visible before the detail: identify what must be decided, define the relevant terms, connect the evidence to chart grammar, and use uncertainty representation to test the result.

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

The controlling limit is specific: Default software output is not a design rationale and an uncertainty band does not explain every source of uncertainty.

Keep that uncertainty representation 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 analytical task, chart grammar and uncertainty representation without notes, explain their relationship aloud, then complete a changed version of the application: choose a chart from the task and data structure, then make uncertainty commensurate with the claim.

Record the first failed chart grammar reasoning move and repair it before attempting another case.

What this chapter covers

• 01

  analytical task

• 02

  chart grammar

• 03

  uncertainty representation

• 04

  Applying analytical task

• 05

  Limits of chart grammar and uncertainty representation

Worked example: Chart Selection, Comparison and Uncertainty

Key terms

analytical task

The operation a viewer must perform, such as locate, compare, rank, associate, distribute or identify change. Use this definition when the task is to choose a chart from the task and data structure, then make uncertainty commensurate with the claim.

chart grammar

A compositional system combining data, statistical transformations, marks, scales, coordinates and facets into a graphic. Use this definition when the task is to choose a chart from the task and data structure, then make uncertainty commensurate with the claim.

uncertainty representation

A visual or textual encoding of measurement error, sampling variation, model range or scenario uncertainty. Use this definition when the task is to choose a chart from the task and data structure, then make uncertainty commensurate with the claim.

Chart Selection, Comparison and Uncertainty FAQ

Assessment move

Reconstruct the relationship among analytical task, chart grammar and uncertainty representation; complete the chapter application without notes; then test the result against this limit: Default software output is not a design rationale and an uncertainty band does not explain every source of uncertainty.

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