Chart Selection Decision Guide

Pick the right chart type based on what you're trying to communicate. This guide covers the 90% case — when in doubt, use a bar chart.

The Decision Framework

Ask yourself: "What relationship am I showing?"

Decision Tree

What are you showing?
│
├─ A single important number?
│  └─ KPI CARD with trend indicator
│
├─ How something changes over time?
│  ├─ Continuous (daily/hourly)? → LINE CHART
│  ├─ Discrete periods (monthly)? → COLUMN CHART
│  └─ Cumulative? → AREA CHART
│
├─ Comparison between categories?
│  ├─ How many categories?
│  │  ├─ 2-5 → GROUPED BAR CHART
│  │  ├─ 6-15 → HORIZONTAL BAR (sorted)
│  │  └─ 15+ → TABLE or TOP-N BAR
│  └─ Part of a whole?
│     ├─ 2-4 parts → DONUT CHART (only exception to no-pie rule)
│     └─ 5+ parts → STACKED BAR (100%)
│
├─ Distribution of values?
│  ├─ One variable? → HISTOGRAM
│  ├─ Compare distributions? → BOX PLOT
│  └─ Density estimation? → VIOLIN PLOT
│
├─ Relationship between variables?
│  ├─ Two continuous? → SCATTER PLOT
│  ├─ Add a third via size? → BUBBLE CHART
│  └─ Many variables? → HEATMAP MATRIX
│
├─ Geographic data?
│  ├─ Regional aggregates? → CHOROPLETH MAP
│  ├─ Point locations? → SYMBOL MAP
│  └─ Routes/flows? → FLOW MAP
│
└─ Progress toward goal?
   ├─ Single metric vs target? → BULLET CHART
   └─ Multiple metrics vs targets? → TABLE with conditional formatting

Chart-Specific Guidelines

Line Charts

• Maximum 5-7 lines before it becomes unreadable
• Always include zero baseline for rate/percentage metrics
• Use solid lines for primary, dashed for comparison/forecast
• Mark significant events with vertical annotation lines
• Show confidence intervals as shaded bands

Bar Charts

• Sort by value (not alphabetical) unless there's a natural order
• Horizontal bars for labels longer than 10 characters
• Space between bars = 40-50% of bar width
• Use a single color unless encoding an additional dimension
• Always start axis at zero (unlike line charts, truncating bars is deceptive)

KPI Cards

Anatomy of a good KPI card:

┌─────────────────────────────┐
│  Revenue (MTD)              │  ← Label + time period
│  $2.4M                      │  ← Big number
│  ▲ 12% vs last month        │  ← Trend with comparison
│  Target: $2.8M              │  ← Context
└─────────────────────────────┘

Tables

• Use tables for detail/lookup, never as the primary visualization
• Right-align numbers, left-align text
• Add conditional formatting (data bars, color scales) for quick scanning
• Limit to 7-10 columns visible at once
• Include sorting and searching

Scatter Plots

• Always label axes clearly (not just field names)
• Add quadrant lines when showing 2x2 framework (high/low segmentation)
• Use size encoding sparingly (humans are bad at comparing areas)
• Color-encode a categorical dimension (max 5-7 categories)
• Add a trend line if showing correlation

Heatmaps

• Use sequential color scale for one-direction data (light → dark)
• Use diverging color scale for data with a meaningful center (red → white → green)
• Sort both axes meaningfully (not alphabetical)
• Include the actual values as text labels if cells are large enough

Color Usage by Chart Type

Common Mistakes by Chart Type

Pie Charts (Almost Always Wrong)

• Problem: Humans cannot accurately compare arc angles or areas
• Exception: Showing 2-3 parts where one dominates (75%/25% split)
• Alternative: Horizontal bar chart, always

Dual-Axis Charts

• Problem: Implies correlation between unrelated metrics; scale manipulation
• When acceptable: Same unit, related metrics (revenue + cost → profit context)
• Alternative: Two charts stacked vertically, aligned on x-axis

Stacked Area Charts

• Problem: Inner bands are hard to read because they don't share a flat baseline
• When acceptable: Showing total composition over time where total matters
• Alternative: Small multiples (one line chart per category)

Treemaps

• Problem: Hard to compare rectangles of similar size; no natural reading order
• When acceptable: Showing hierarchical part-of-whole with 2+ levels
• Alternative: Sunburst diagram or nested horizontal bars

Dashboard Layout Patterns

Pattern 1: KPI + Trend + Detail (Most Common)

┌──────────┬──────────┬──────────┬──────────┐
│  KPI 1   │  KPI 2   │  KPI 3   │  KPI 4   │  ← Status row
├──────────┴──────────┴──────────┴──────────┤
│                                            │
│           Main Trend Chart                 │  ← Analysis
│                                            │
├─────────────────────┬──────────────────────┤
│  Breakdown Chart 1  │  Breakdown Chart 2   │  ← Detail
├─────────────────────┴──────────────────────┤
│              Detail Table                   │  ← Export
└────────────────────────────────────────────┘

Pattern 2: Comparison Layout

┌──────────────────────┬─────────────────────┐
│   Current Period     │   Previous Period    │  ← Side by side
├──────────────────────┴─────────────────────┤
│              Variance Chart                  │  ← What changed
├────────────────────────────────────────────┤
│              Top Movers Table               │  ← Biggest changes
└────────────────────────────────────────────┘

Pattern 3: Funnel / Journey Layout

┌────────────────────────────────────────────┐
│              Funnel Visualization           │  ← The flow
├────────────┬───────────────┬───────────────┤
│  Stage 1   │   Stage 2     │   Stage 3     │  ← Stage details
│  Metrics   │   Metrics     │   Metrics     │
├────────────┴───────────────┴───────────────┤
│           Drop-Off Analysis                 │  ← Where we lose them
└────────────────────────────────────────────┘

Pattern 4: Geographic Layout

┌─────────────────────────┬──────────────────┐
│                         │  Region KPIs     │
│       Map               │  ┌────────────┐  │
│                         │  │ North: $2M  │  │
│                         │  │ South: $1M  │  │
│                         │  └────────────┘  │
├─────────────────────────┴──────────────────┤
│           Regional Trend Chart              │
└────────────────────────────────────────────┘

Tool-Specific Recommendations

Tableau

• Use container-based layouts for responsive behavior
• Leverage parameter actions for interactivity without separate filter controls
• Small multiples via row/column shelves, not duplicated worksheets
• Use Level of Detail (LOD) expressions instead of table calculations when possible

Looker

• Single-value tiles for KPIs with value_format for readability
• Use listen filters to link tiles, not cross-filtering
• Merged results for combining explores in one tile
• Dashboard-level filters with required_fields for performance

Power BI

• Use bookmarks for guided navigation between views
• Sync slicers across pages for consistent filtering experience
• Custom tooltips for progressive disclosure on hover
• Field parameters for user-controlled measure switching