data-visualization-designer

name	data-visualization-designer
description	Provides expert design guidance for creating truthful, clear, beautiful data visualizations. Focuses on **DESIGN DECISIONS ONLY**—chart selection, color strategy, visual encoding, and validation. Assumes data is accurate and prepared. Auto-activates when user mentions: data viz, dashboard, chart type, visualization, infographic

Data Visualization Designer

MANDATORY PRE-WORK CHECKLIST

YOU MUST complete this checklist BEFORE applying this skill:

[ ] 1. Read Task Decomposition Override Section

• WHY: Understand the PROHIBITED sequence (Implementation-First Antipattern)
• WHY: Understand the MANDATORY sequence (Design-Decision Framework with 4 critical decisions)
• CONSEQUENCE: Skipping = 30-50% redesign waste + accessibility failures + misleading visualizations

[ ] 2. Acknowledge Output Format Requirement

• FORMAT REQUIRED:

  Data Viz Design Applied:
  - Brief: [Purpose + Audience + Success metric]
  - Chart Type: [Type] because [data structure + task]
  - Color: [Sequential/Diverging/Categorical] palette, [redundant encoding method]
  - Encoding: [Primary variable] → position, [Secondary] → [channel]
  

• WHY: Hook validation requires this exact format
• CONSEQUENCE: Missing acknowledgment = architecture violation

[ ] 3. Identify Data Viz-Specific Requirements

• Chart Type Justification: Chart MUST match data structure AND task (NOT aesthetics or "what looks cool")
• Color Accessibility: NO red-green only encoding, MUST use redundant channels (color + shape/pattern/label)
• Truthfulness Validation: Y-axis starts at zero (bar charts) OR clearly labeled, no truncated axes to exaggerate
• Perceptual Hierarchy: Position > Length > Angle > Area > Color (Cleveland & McGill research)
• Colorblind Safe: Blue-Orange or Blue-Yellow palettes, test with simulators
• WHY: Wrong chart type + color-only encoding + misleading axes = 83.5% viewer misinterpretation
• CONSEQUENCE: Ignoring = unusable visualization that actively misleads decision-makers

[ ] 4. Check for Multi-Skill Compositions (v5.5.0)

• IF data-visualization-designer + design-excellence + diagram-drawing loaded:
  • YOU MUST apply all three skills in conjunction (not isolation)
  • Composition: visual-design-excellence (3.2x quality improvement)
  • This skill = data encoding decisions, design-excellence = aesthetics, diagram = Chart.js code
• CONSEQUENCE: Single-skill usage when composition available = suboptimal quality

✅ ALL BOXES CHECKED = Ready to proceed to Task Decomposition Override ❌ SKIPPING THIS CHECKLIST = Claiming "Data Viz Design Applied" while creating misleading charts

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Task Decomposition Override (v5.4.0)

When designing data visualizations, DO NOT use your default task decomposition.

❌ PROHIBITED SEQUENCE (Implementation-First Antipattern):

1. Jump straight to creating charts
2. Pick chart type based on aesthetics
3. Apply colors randomly
4. Add data and hope it works
5. Discover accessibility issues after completion

Consequence: Redesign waste (30-50% rework), accessibility failures, misleading visualizations, frustrated stakeholders.

✅ MANDATORY SEQUENCE (Design-Decision Framework):

Phase 1: Design Decision (Make 4 critical decisions)

1. Establish Brief:

   • Reference: Skill "The Foundation: Four-Element Framework"
   • Output: Purpose, audience, context, success metric documented

2. Select Chart Type:

   • Reference: Skill "Chart Type Selection" + @data-visualization-designer/resources/perceptual-accuracy-research.md
   • Output: Chart type with justification (comparison/relationship/distribution/composition)

3. Design Color Strategy:

   • Reference: Skill "Color Strategy"
   • Output: Palette type (sequential/diverging/categorical), colorblind-safe verification, redundant encoding plan

4. Plan Visual Encoding:

   • Reference: @data-visualization-designer/resources/perceptual-accuracy-research.md
   • Output: Which visual channels encode which variables (position > length > color)

Output Acknowledgment After Phase 1:

Data Viz Design Applied:
- Brief: [Purpose + Audience + Success metric]
- Chart Type: [Type] because [data structure + task]
- Color: [Sequential/Diverging/Categorical] palette, [redundant encoding method]
- Encoding: [Primary variable] → position, [Secondary] → [channel]

Phase 2: Implementation (Apply decisions)

5. Apply typography hierarchy (reference: @data-visualization-designer/resources/crap-principles-for-data.md)
6. Add strategic annotations (reference: @data-visualization-designer/resources/data-storytelling.md)
7. Optimize data-ink ratio (reference: @data-visualization-designer/resources/data-ink-optimization.md)
8. Implement design (hand off to diagram-drawing skill for Chart.js/D3.js code)

Phase 3: Validation (Verify quality)

9. Run truthfulness audit (reference: Skill "Critical Mistakes" - Fatal category)
10. Check accessibility (reference: Skill "Accessibility Requirements")
11. Validate against Quick Audit Checklist (reference: Skill "Quick Audit Before Publishing")

IF you use ❌ sequence instead of ✅ sequence = ARCHITECTURE VIOLATION

Rationale: Design decisions BEFORE implementation prevents 30-50% redesign waste. Establishes brief, justifies chart selection, ensures accessibility from start, enables validation against documented criteria. Quality guaranteed through checkable Phase 1 outputs.

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Language Standards (v5.4.0)

YOU MUST use directive language throughout:

• ✅ "YOU MUST use", "DO NOT use", "ALWAYS", "NEVER", "MANDATORY", "PROHIBITED"
• ❌ Never: "should", "consider", "might", "could", "try to"

Enforcement: Skills with weak language blocked by pre-tool-use-write.ts hook.

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The Foundation: Four-Element Framework

Every effective visualization requires these elements:

Information - Accurate, verified data (provided to you)

Story - The insight your visualization communicates

Goal - Specific purpose: persuade, enable decisions, communicate insights

Visual Form - How you encode meaning through visual channels (position, color, size, shape)

YOU MUST establish all four elements before designing. If any element is unclear, use AskUserQuestion tool to clarify. Missing elements create incomplete, ineffective visualizations.

Brief Template

Answer these before starting:

Purpose: What specific question does this answer? What decision should it enable?

Audience: Who views this? Technical experts or general public? Visual literacy level?

Context: When/how will viewers access? Dashboard? Report? Publication? Mobile or desktop?

Success Metric: How do you know it succeeded? Comprehension in 5 seconds? Action taken? Decision made?

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Chart Type Selection

YOU MUST match chart type to data structure and task, NOT aesthetics.

COMPARISON (How datasets differ)

Few values (≤3): Bar/column chart Many values (4-10): Grouped bars or dot plot Many categories (>10): Horizontal bar chart (easier label reading) Time-based comparison: Column chart

❌ AVOID: Pie charts (human vision terrible at comparing angles—10-30× less accurate than bars)

RELATIONSHIP (How variables correspond)

Two continuous variables: Scatter plot Three dimensions: Bubble chart (size = 3rd variable) Many comparisons: Small multiples Correlation strength: Scatter plot with regression line

❌ AVOID: Lines connecting scatter points (implies false temporal continuity)

DISTRIBUTION (How data spreads)

Single variable distribution: Histogram or box plot Distribution over time: Line chart Multiple distributions: Small multiples or violin plots Pattern matrix: Heatmap

❌ AVOID: 3D histograms (distorts perception), rainbow colormaps (creates false boundaries)

COMPOSITION (Parts of whole)

Static 2-5 categories: Stacked bar chart (NOT pie) Changes over time: Stacked area chart or waterfall Hierarchical data: Treemap or sunburst Flow between categories: Sankey diagram

❌ AVOID: Pie charts except rare cases (<5 categories, one slice >50%)

Decision Matrix

Data Structure	Task	Recommended Chart
1 categorical, 1 quantitative	Compare values	Bar chart
2 categorical, 1 quantitative	Compare groups	Grouped/stacked bar
Time series, 1 metric	Show trend	Line chart
Time series, multiple metrics	Compare trends	Multiple lines or small multiples
2 continuous variables	Correlation	Scatter plot
1 continuous variable	Distribution	Histogram
Hierarchical categories	Part-whole	Treemap
Geographic data	Spatial patterns	Choropleth map

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Color Strategy

YOU MUST use color to serve a communication goal, NOT decoration. Reserve saturated colors for emphasis.

Choose Palette Type

Sequential (single hue, light to dark) - Ordered data

• Use for: Heatmaps, distributions, intensity, magnitude
• Safe palettes: Viridis, Blues, Grays, YlGnBu
• ❌ AVOID: Rainbow/Jet (creates false boundaries, colorblind-hostile)

Diverging (two sequences, neutral center) - Meaningful midpoint

• Use for: Temperature anomalies, profit/loss, deviations from mean, +/- data
• Safe palettes: Blue-White-Orange, Green-White-Purple, RdBu
• ❌ AVOID: Red-Green together (~8% of viewers can't distinguish)

Categorical (distinct groups) - Unrelated categories

• Use for: 2-7 categories maximum
• Safe palette: Orange, Blue, Green, Red, Purple, Yellow, Gray (in priority order)
• ❌ AVOID: Too many colors (>7 overwhelms memory), similar hues (hard to distinguish)

Accessibility Requirements (MANDATORY)

YOU MUST implement ALL of these:

1. Never rely on color alone → Add labels, patterns, shapes, or text
2. Never red-green together → ~8% of viewers (1 in 12 men) cannot distinguish
3. Always check grayscale → Visualization must work in black and white
4. Always add redundant encoding → Color + label, or color + pattern, or color + shape

Colorblind-safe palettes:

• Blue-Orange (most universal)
• Blue-Yellow
• Purple-Orange
• Viridis/Plasma (perceptually uniform, colorblind-friendly)

Test your palette: Use colorblind simulation tools (Coblis, Color Oracle) to verify.

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Typography & Visual Hierarchy

Font Selection:

• YOU MUST use: Sans-serif fonts for screen legibility (IBM Plex Sans, Space Grotesk, Source Sans 3, Fira Sans)
• ❌ DO NOT use: Inter, Roboto, Arial, Helvetica (signals "AI slop"—generic AI-generated content)
• Limit: 2 fonts maximum (heading + body)
• Weight: Regular weight default (not light, not bold except emphasis)

Size Hierarchy (establish clear levels):

• Title: Largest, boldest (18-24pt, dominant message)
• Axis labels: Secondary (12-14pt)
• Annotations: Tertiary (10-12pt)
• Minimum: 12pt on screen, 10pt in print

Apply CRAP Principles (reference: @data-visualization-designer/resources/crap-principles-for-data.md):

• Contrast: Different elements very different (size, color, weight)
• Repetition: Same font/color/size for same element types (coherence)
• Alignment: Every element connects visually to another
• Proximity: Related items grouped close; unrelated separated

Whitespace Strategy: Strategic blank space directs attention and reduces cognitive load. DO NOT fear empty areas—they create breathing room.

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Visual Encoding Hierarchy

Based on Cleveland & McGill perceptual accuracy research (reference: @data-visualization-designer/resources/perceptual-accuracy-research.md):

Perceptual Accuracy Ranking (Most to Least Accurate)

1. Position along common scale (X/Y axis) - MOST ACCURATE
2. Position on non-aligned scales (small multiples)
3. Length (bar heights)
4. Angle (pie slices) - 2-3× less accurate than position
5. Area (bubble size) - hard to judge, non-linear perception
6. Volume (3D objects) - highly inaccurate, distorted
7. Color saturation - LEAST ACCURATE for quantities

Design Implications

YOU MUST apply this hierarchy:

• Put most important comparisons in position along axis (highest accuracy)
• Use length for secondary comparisons (bar charts, column charts)
• Use color for emphasis or categorization (NOT for precise quantities)
• NEVER use 3D for non-spatial data (distorts perception, reduces accuracy)

Example: Comparing sales across regions over time

• Position: Time on X-axis, sales on Y-axis (primary comparison)
• Color: Different regions (categorical distinction)
• ❌ NOT area: Bubble size for sales (hard to judge precisely)

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Annotation & Storytelling

Strategic annotations explain and guide (reference: @data-visualization-designer/resources/data-storytelling.md).

What to Annotate

YOU MUST annotate:

• Outliers and anomalies - Why is this point unusual?
• Historical context - Benchmarks, previous periods, goals
• Key findings - Insights you want highlighted
• Methodology - Data source, date range, limitations

Keep concise: One insight per annotation. Style consistently. Avoid over-annotation (more annotations than data points = clutter).

Direct Labeling Strategy

YOU MUST use direct labeling instead of legends whenever possible:

• Integrate labels into visualization
• Eliminates need to match colors back to legend
• Reduces cognitive load
• Faster comprehension

Example: Label each line directly at endpoint instead of legend box.

Title Conveys Insight

❌ Descriptive title: "Sales Over Time" ✅ Insight-driven title: "Sales Increased 60% in Q4" ✅ Question-answering title: "Which Products Drive Growth? Premium Segment"

Title should communicate main takeaway without requiring viewers to read the full chart.

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Critical Mistakes to Avoid

❌ FATAL (Directly Misleads Viewers)

Truncated Y-Axes on Bar Charts

• What it is: Y-axis doesn't start at zero, exaggerates differences
• Impact: 83.5% of viewers misinterpret magnitude (Cleveland & McGill)
• Fix: ALWAYS start bar chart Y-axes at zero, OR use broken axis indicator + clear labeling

3D Effects (Non-Spatial Data)

• What it is: Adding depth/perspective to charts representing non-spatial data
• Impact: Distorts through perspective (lie factor 1.5-2.0), rear values appear smaller
• Fix: NEVER use 3D for business/analytical data

Red-Green Color Encoding

• What it is: Using red and green as primary color distinction
• Impact: ~8% of viewers (1 in 12 men) see both as same muddy color
• Fix: Use Blue-Orange, Blue-Yellow, or other colorblind-safe palettes + redundant encoding

⚠️ SERIOUS (Significantly Reduce Effectiveness)

Rainbow Colormap (Jet)

• What it is: Rainbow gradient (red-orange-yellow-green-blue-purple)
• Impact: Creates false boundaries (bright yellow stripe), non-monotonic luminance, colorblind-hostile
• Fix: Replace with Viridis, Plasma, or Blue-White-Red diverging palette

Color-Only Encoding

• What it is: Information conveyed ONLY by color, no alternative
• Impact: Fails for colorblind viewers, grayscale printing, accessibility
• Fix: Add direct labels, patterns, shapes, or text (redundant encoding)

Dual-Axis Charts (Incompatible Scales)

• What it is: Two Y-axes with different scales on same chart
• Impact: Creates false correlation appearance, easily manipulated
• Fix: Use separate charts instead, OR ensure scales proportional + clearly labeled

Pie Charts for Comparisons

• What it is: Using pie charts to compare multiple values
• Impact: Human vision terrible at comparing angles (10-30× less accurate than bars)
• Fix: Use bar charts for comparison; pie only for showing one slice >50%

📊 MODERATE (Reduce Clarity)

Too Many Colors (>7)

• Impact: Overwhelms viewers, exceeds working memory capacity
• Fix: Reduce to 5-7 max, combine minor categories into "Other"

Missing Context

• Impact: No title, axis labels, data source, or date → viewers can't interpret or trust
• Fix: ALWAYS include title (conveys insight), axis labels (with units), source, date

Chartjunk (reference: @data-visualization-designer/resources/data-ink-optimization.md)

• Impact: Heavy gridlines, 3D effects, decorative backgrounds, ornamental fonts increase cognitive load
• Fix: Remove all non-data elements; maximize data-ink ratio

Small Text

• Impact: Below 12pt struggles for readability, excludes people with low vision
• Fix: Minimum 12pt (14pt+ optimal for accessibility)

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Quick Audit Before Publishing

Run this 9-minute checklist before sharing any visualization:

Data Integrity (2 minutes)

• Bar chart Y-axis starts at zero OR clearly labeled if not
• No 3D effects on non-spatial data
• Dual axes proportional or clearly explained
• Data truthfully represented (no distortion)

Design Quality (3 minutes)

• Title conveys insight (not just "Chart")
• Axis labels include units
• Color palette limited (max 5-7 categorical)
• No red-green together
• No color-only encoding (redundant encoding added)
• Grayscale readable

Context (2 minutes)

• Title clear and insight-driven
• Legend present OR direct labels used
• Data source and date cited
• Sufficient context for interpretation
• Key findings/outliers explained

Polish (2 minutes)

• Font professional sans-serif (IBM Plex Sans, Space Grotesk, Source Sans 3, NOT Inter/Roboto)
• Text minimum 12pt
• Alignment consistent (CRAP principles applied)
• Whitespace strategic
• No chartjunk (reference: data-ink-optimization.md)

Total: 9 minutes. All checkboxes pass = ready to publish.

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Integration

Works Well With:

• Skill: design-excellence - General typography anti-patterns, color theory, motion principles, background design (auto-activates together)
• Skill: diagram-drawing - Chart.js/D3.js technical implementation, export to PNG/SVG/PDF (auto-activates together)
• Pattern: component_design - UI component design patterns

Typical Workflow:

1. design-excellence auto-activates → General design principles (typography, color themes)
2. data-visualization-designer auto-activates → Chart selection, color strategy, validation
3. diagram-drawing auto-activates → Chart.js implementation code

Separation of Concerns:

• design-excellence = General design (not data-specific)
• data-visualization-designer = Design decisions (what chart, why, validation)
• diagram-drawing = Technical execution (Chart.js config, D3.js patterns)

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When to Load Resources

CRAP principles deep-dive:

• @data-visualization-designer/resources/crap-principles-for-data.md - Contrast, Repetition, Alignment, Proximity applied to charts/dashboards

Perceptual accuracy research:

• @data-visualization-designer/resources/perceptual-accuracy-research.md - Cleveland & McGill hierarchy, encoding decisions, science-backed design

Data-ink optimization:

• @data-visualization-designer/resources/data-ink-optimization.md - Tufte principles, chartjunk removal, maximizing data-ink ratio

Storytelling techniques:

• @data-visualization-designer/resources/data-storytelling.md - Annotation strategies, narrative arc, progressive disclosure

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Anti-Patterns to Avoid

Chart Selection:

• ❌ Pie charts for comparison tasks (use bar charts)
• ❌ 3D charts for non-spatial data (use 2D)
• ❌ Dual-axis with incompatible scales (use separate charts)
• ❌ Lines connecting non-temporal scatter points (remove lines)

Color:

• ❌ Red-green encoding (~8% can't distinguish)
• ❌ Rainbow/Jet colormap (creates false boundaries)
• ❌ Color-only encoding (add redundant labels/patterns)
• ❌ Too many colors (>7 overwhelms memory)
• ❌ Purple gradients on white (cliché "AI slop" pattern)

Typography:

• ❌ Inter, Roboto, Arial, Helvetica fonts (signals generic AI content)
• ❌ All text same size/weight (no hierarchy)
• ❌ Text below 12pt (readability issues)
• ❌ Ornamental fonts (reduces legibility)

Truthfulness:

• ❌ Truncated Y-axis without clear indication (misleads magnitude)
• ❌ 3D effects (distorts perception)
• ❌ Manipulated scales (exaggerates differences)
• ❌ Cherry-picked data ranges (hides context)

Layout:

• ❌ Missing axis labels/units (viewers can't interpret)
• ❌ No title or generic title (doesn't convey insight)
• ❌ No data source or date (can't verify or trust)
• ❌ Chartjunk (heavy gridlines, decorative backgrounds, borders)
• ❌ Pure white (#fff) or pure black (#000) backgrounds (use atmospheric gradients)

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Design Checklist

Before implementing any visualization, verify all 8:

1. ✓ Brief Established - Purpose, audience, context, success metric clear
2. ✓ Chart Type Selected - Matched to data structure and task, justified over alternatives
3. ✓ Color Strategy Decided - Palette type chosen (sequential/diverging/categorical), accessibility verified, redundant encoding planned
4. ✓ Visual Hierarchy Clear - Title dominant, axis labels secondary, annotations tertiary, whitespace strategic
5. ✓ Encoding Optimized - Most important variables in highest-accuracy channels (position > length > color)
6. ✓ Annotations Complete - Key insights highlighted, context provided, outliers explained
7. ✓ Accessibility Verified - No color-only encoding, grayscale works, no red-green, text ≥12pt, redundant encoding present
8. ✓ Mistakes Avoided - Passed Fatal/Serious/Moderate audit, 9-minute quick audit completed

All 8 passing = ready to implement (hand off to diagram-drawing skill for Chart.js/D3.js code).

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Core Principle

Truthfulness > Beauty > Novelty

Always.

Design emerges from understanding:

1. The data (structure, patterns, limitations)
2. The insight you want to communicate
3. The audience who needs to understand it

Rush any of these = poor design. 80% effort → understanding. 20% effort → visual execution.