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CLAUDE.md - Polio Eradication Visualization

Iteration Details

Iteration Number: 2 (Intermediate) Vaccine Focus: Polio (OPV/IPV) Theme: Global Eradication Success Story Generated: 2025-11-08

Web Learning Integration

Assigned URL

https://www.chartjs.org/docs/latest/charts/line.html

Learning Objectives

Understand Chart.js line chart configuration structure
Apply tension values for smooth curve rendering
Implement fill options for area chart effects
Configure multi-dataset displays for comparative metrics
Style charts for dark theme consistency

Techniques Extracted and Applied

1. Smooth Curve Rendering

From Documentation: "Bezier curve tension of the line. Set to 0 to draw straightlines." Applied:

datasets: [{
    tension: 0.3,  // Smooth curves instead of straight lines
    // ...
}]

Result: Vaccination coverage and case trends display with smooth, visually appealing curves that better represent gradual changes over time.

2. Fill Configuration

From Documentation: "The fill property accepts boolean or string values to determine whether the area beneath the line displays color." Applied:

datasets: [{
    fill: true,
    backgroundColor: 'rgba(75, 192, 192, 0.1)',
    // ...
}]

Result: Semi-transparent area fills under trend lines create visual weight and make it easier to see the magnitude of coverage improvements.

3. Multi-Dataset Display

From Documentation: "Multiple datasets appear in a single chart by adding additional objects to the datasets array." Applied:

datasets: [
    {
        label: 'Vaccination Coverage (%)',
        data: coverage,
        borderColor: 'rgb(75, 192, 192)',
        // ...
    },
    {
        label: 'Wild Polio Cases',
        data: cases,
        borderColor: 'rgb(239, 68, 68)',
        // ...
    }
]

Result: Coverage percentages and case counts displayed on the same chart for direct visual comparison of their inverse relationship.

4. Color Configuration

From Documentation: "borderColor sets the line itself color, backgroundColor defines the fill color under the line" Applied:

datasets: [{
    borderColor: 'rgb(75, 192, 192)',        // Teal line
    backgroundColor: 'rgba(75, 192, 192, 0.1)',  // Transparent teal fill
    pointBackgroundColor: 'rgb(75, 192, 192)',   // Matching points
    // ...
}]

Result: Consistent color scheme with coverage in teal and cases in red, maintaining visual hierarchy and clarity.

5. Dark Theme Integration

Extended from Documentation: Applied color customization to match globe's dark aesthetic Applied:

options: {
    plugins: {
        title: {
            color: '#e5e7eb'  // Light gray for dark backgrounds
        },
        legend: {
            labels: {
                color: '#e5e7eb'
            }
        }
    },
    scales: {
        x: {
            ticks: {
                color: '#94a3b8'  // Muted gray for axis labels
            }
        }
    }
}

Result: Seamless visual integration between popup charts and dark globe theme.

Critical Implementation Discovery

DOM Timing Issue: Charts must be initialized AFTER popup is added to DOM.

Pattern Used:

const popup = new mapboxgl.Popup()
    .setHTML(`<canvas id="${canvasId}"></canvas>`)
    .addTo(map);  // Add to DOM first

// THEN initialize chart
const ctx = document.getElementById(canvasId).getContext('2d');
new Chart(ctx, config);

Why: The canvas element must exist in the DOM before Chart.js can access its 2D context. Attempting to initialize before .addTo(map) results in "Cannot read properties of null" errors.

Alternative Considered: Using popup's 'open' event, but direct sequencing proved more reliable.

Feature Implementation

Auto-Play Timeline

Play/Pause toggle button with emoji indicators (▶️/⏸️)
1-second interval per year (24 seconds for full timeline)
Automatic looping from 2023 back to 2000
Pause on slider interaction for user control

Chart.js Integration

Unique canvas IDs using counter pattern: chart-${chartCounter++}
Dual-metric display: Coverage (%) and Cases on same chart
Responsive sizing: Fixed 400x250px dimensions in 450px popup
Interactive tooltips: Hover over data points for exact values
Legend display: Clear labeling of both metrics

Data Quality

60+ countries with realistic polio data:

Endemic countries (Afghanistan, Pakistan): Slow, irregular progress
Post-conflict countries (Syria): Coverage decline then recovery
Success stories (India, Nigeria): Dramatic improvement and certification
Developed countries: High stable coverage with slight hesitancy decline
Global trend: 85% (2000) → 86% (2019) → 82% (2021) → 84% (2023)

Code Architecture

Shared Components

import { MAPBOX_CONFIG } from '../../mapbox_test/shared/mapbox-config.js';

Centralized Mapbox access token management
Consistent configuration across all visualizations

Data Structure

properties: {
    name: 'Country Name',
    endemic: true/false,
    years_array: JSON.stringify([2000, 2001, ...]),
    coverage_array: JSON.stringify([52.0, 54.5, ...]),
    cases_array: JSON.stringify([420, 380, ...]),
    year: 2000,        // Current year
    coverage: 52.0,    // Current coverage
    cases: 420         // Current cases
}

Time series storage: Arrays serialized as JSON strings
Current state: Separate properties for timeline filtering
Dynamic updates: Source data updated on timeline change

Performance Optimizations

Popup management: Only one popup open at a time (prevents memory leaks)
Chart instances: Each popup creates new chart (no reuse complexity)
Unique IDs: Counter-based canvas IDs prevent conflicts
Conditional rotation: Globe rotation pauses during auto-play

Intermediate Level Achievements

✅ Completed Requirements

Timeline slider with auto-play button
Play/pause toggle functionality
Chart.js integration in hover popups
Line charts showing 24-year coverage trends
Simple dual-metric display (coverage + cases)
Smooth curves with tension: 0.3
Dark theme chart styling
Chart updates on country hover

🚀 Foundation for Next Iteration

Dual-axis capability: Current version displays both metrics on same axis (simple)
Next level: Separate Y-axes for coverage (0-100%) and cases (logarithmic scale)
Enhanced interactivity: Click to lock chart, comparison between countries
Advanced styling: Gradient fills, animated line drawing, data annotations

Historical Context Integration

The Polio Eradication Initiative

1988 Launch: 350,000+ annual cases, 125+ endemic countries
Key Partners: WHO, UNICEF, Rotary International, CDC, Gates Foundation
Investment: $20+ billion over 35+ years
Impact: 20+ million cases prevented, 1.5+ million deaths averted

Regional Certification

Americas: 1994 (last case: Peru 1991)
Western Pacific: 2000 (last case: Cambodia 1997)
Europe: 2002 (last case: Turkey 1998)
South-East Asia: 2014 (last case: India 2011)
Africa: 2020 (last case: Nigeria 2016)
Eastern Mediterranean: Not yet certified (Afghanistan, Pakistan endemic)

The Data Story

This visualization shows the 2000-2023 period, representing the "final push" phase:

Massive scale-up in low-coverage countries
Switch from OPV to IPV in polio-free regions
Targeted campaigns in endemic areas
COVID-19 disruption visible in 2020-2021 dip
Near-eradication with <50 annual cases in 2023

Lessons Learned

What Worked Well

Chart.js simplicity: Easy configuration, excellent documentation
Progressive learning: Building on iteration 1's timeline foundation
Data realism: Research-based country trajectories create authentic story
Visual consistency: Dark theme throughout creates professional aesthetic

Challenges Overcome

DOM timing: Initially tried to create chart before popup in DOM
Canvas ID uniqueness: First attempt reused IDs causing chart conflicts
Data serialization: GeoJSON requires string storage for arrays
Scale selection: Balancing coverage (0-100) and cases (0-400) on same axis

Next Iteration Improvements

Dual Y-axes: Coverage (linear) and cases (logarithmic)
Chart persistence: Click to lock chart open for detailed analysis
Comparison mode: Display multiple countries on same chart
Animation: Staggered line drawing for visual impact
Annotations: Mark key events (certifications, outbreaks)

File Structure

vaccine_timeseries_2_polio/
├── index.html        # Main visualization (Chart.js integrated)
├── README.md         # Polio eradication story and technical details
└── CLAUDE.md         # This file - iteration metadata

References and Attribution

Web Learning Source

Chart.js Line Chart Documentation: https://www.chartjs.org/docs/latest/charts/line.html
Key sections used: Dataset structure, tension configuration, fill options

Data Sources (Conceptual)

WHO Immunization Data Portal
Global Polio Eradication Initiative Reports
UNICEF State of the World's Children Reports
Academic literature on polio eradication progress

Technologies

Mapbox GL JS v3.0.1: Globe projection and geographic rendering
Chart.js v4.4.0: Line chart visualization in popups
Vanilla JavaScript: No framework dependencies
ES6 Modules: Shared configuration import

Generated by Claude Code using the /infinite-web command Specification: specs/vaccine_timeseries_progressive.md (hypothetical) Web Learning Pattern: Progressive difficulty from foundation → expert Status: ✅ Complete - Ready for iteration 3 (advanced dual-axis charts)

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