# Globe Visualization 4: Global Digital Infrastructure

**Multi-Layer Mapbox Globe Visualization - Iteration 4**

This is the fourth iteration in a progressive learning series demonstrating advanced Mapbox GL JS techniques with globe projection. This iteration synthesizes all previous learnings and introduces multi-layer composition with choropleth maps.

## 🌍 Theme: Global Digital Infrastructure & Connectivity

This visualization showcases the global digital landscape by combining multiple data layers:

- **Internet penetration rates** by country (choropleth/fill layer)
- **Major tech hubs and internet exchange points** (circle layer)
- **International connectivity links** between major hubs (line layer)
- **City labels** for top-tier tech centers (symbol layer)

## 📚 Learning Progression

### Previous Iterations:
1. **Iteration 1**: Population circles - Single layer visualization with basic circle styling
2. **Iteration 2**: Temperature heatmap - Single layer with heatmap type and color gradients
3. **Iteration 3**: Economic data-driven styling - Advanced expressions and conditional styling
4. **Iteration 4** (this): Multi-layer composition synthesizing all techniques

## 🔬 Web-Enhanced Learning

**Research Source**: Mapbox GL JS Choropleth Documentation
**URL**: https://docs.mapbox.com/mapbox-gl-js/example/updating-choropleth/

### Key Choropleth Techniques Learned:

1. **Fill Layer Configuration**
   - Using `type: 'fill'` for geographic region visualization
   - Applying filters to show/hide specific features
   - Managing multiple fill layers with different zoom levels

2. **Data-Driven Styling**
   - `interpolate` expressions for smooth color gradients
   - Linear color scales mapping data values to visual properties
   - Dynamic paint properties based on feature attributes

3. **Layer Composition**
   - Combining fill, circle, line, and symbol layers
   - Managing layer order and visibility
   - Coordinating opacity across multiple layers

4. **Interactive Features**
   - Zoom-based layer visibility
   - Dynamic legend updates
   - Filter-based layer management

## 🎨 Multi-Layer Architecture

### Layer 1: Country Choropleth (Fill as Circles)
- **Data**: 100+ countries with internet penetration percentages
- **Styling**: Color interpolation from red (low) to green (high)
- **Features**: Data-driven circle sizing based on population
- **Expression**: Linear interpolation across 8 color stops (0-100%)

### Layer 2: Tech Hub Circles
- **Data**: 80 major tech cities and internet exchange points
- **Styling**: Size based on importance score (4-18px radius)
- **Colors**:
  - Tech Hubs: #4ecdc4 (cyan)
  - Internet Exchanges: #ff6b6b (red)
- **Expression**: Categorical matching for hub types

### Layer 3: Connection Lines
- **Data**: International links between Tier 1 hubs (importance ≥ 85)
- **Styling**: Gradient lines with data-driven width
- **Features**: Line gradient from cyan to green
- **Expression**: Width based on connection strength (400-1000 range)

### Layer 4: City Labels
- **Data**: Labels for top tech hubs (importance ≥ 75)
- **Styling**: Size scaled by importance (10-14px)
- **Features**: White text with black halo for readability

## 🎛️ Advanced Features

### Interactive Controls

**Layer Toggles**:
- Show/hide countries, cities, connections, and labels independently
- Real-time layer visibility management

**Filter Controls**:
- **Region Filter**: View specific continents (6 regions + all)
- **Metric Filter**: Switch between internet penetration and digital index
- Dynamic legend updates based on selected metric

**Opacity Sliders**:
- Independent opacity control for each layer type
- Real-time visual feedback with percentage display
- Range: 0-100% for fine-tuned transparency

### Visual Design

**Color Schemes**:
- **Internet Penetration**: 8-stop gradient (red → yellow → green)
- **Digital Index**: 4-stop grayscale gradient
- **Tech Hubs**: Cyan for hubs, red for exchanges
- **Connections**: Cyan-to-green gradient lines

**Globe Features**:
- Atmosphere with space-color and star-intensity
- Auto-rotation when not interacting
- Smooth transitions between data views

### Data Visualization

**Country Data** (100+ countries):
- Internet penetration: 15-99%
- Digital infrastructure index: 25-95
- Population: 1.2M - 1.4B
- Regional grouping: 6 regions

**City Data** (80 tech hubs):
- Tier 1 (90-100): 8 global capitals
- Tier 2 (75-89): 16 major centers
- Tier 3 (60-74): 26 emerging cities
- Tier 4 (45-59): 30 regional centers

**Connection Network**:
- Automatic generation between Tier 1 hubs
- Cross-country connections only
- Strength-based line width

## 🔧 Technical Implementation

### Multi-Layer Composition Pattern

```javascript
// Layer ordering (bottom to top):
1. country-fills (choropleth base)
2. hub-connections (lines)
3. tech-hubs (circles)
4. city-labels (symbols)
```

### Data-Driven Expression Examples

**Choropleth Color Interpolation**:
```javascript
'circle-color': [
  'interpolate',
  ['linear'],
  ['get', 'internetPenetration'],
  0, '#cc0000',    // Dark red
  30, '#ff3300',   // Red-orange
  50, '#ff9900',   // Orange
  70, '#33cc33',   // Light green
  90, '#004d00'    // Dark green
]
```

**Size-Based Scaling**:
```javascript
'circle-radius': [
  'interpolate',
  ['linear'],
  ['get', 'importance'],
  45, 4,   // Small cities
  75, 9,   // Medium cities
  100, 18  // Major hubs
]
```

**Categorical Styling**:
```javascript
'circle-color': [
  'match',
  ['get', 'type'],
  'Internet Exchange', '#ff6b6b',
  'Tech Hub', '#4ecdc4',
  '#95e1d3'  // fallback
]
```

### Filter Implementation

**Region-Based Filtering**:
```javascript
// Countries
map.setFilter('country-fills', ['==', ['get', 'region'], region]);

// Cities (join with country data)
const regionCountries = countriesData.features
  .filter(f => f.properties.region === region)
  .map(f => f.properties.country);
map.setFilter('tech-hubs', ['in', ['get', 'country'], ['literal', regionCountries]]);
```

## 📊 Statistics Dashboard

**Global Metrics Display**:
- Total countries: 100+
- Average internet penetration: ~66%
- Total tech hubs: 80
- Tier 1 hubs: 8
- International links: Dynamic count

## 🎯 Synthesis of Learning

This visualization demonstrates cumulative mastery of:

1. **From Iteration 1**: Circle layer fundamentals, basic styling, globe projection
2. **From Iteration 2**: Color gradients, data-driven opacity, visual layering
3. **From Iteration 3**: Advanced expressions, conditional styling, property matching
4. **New in Iteration 4**:
   - Multi-layer composition and ordering
   - Choropleth/fill techniques adapted for circles
   - Layer visibility management
   - Cross-layer filtering and coordination
   - Multiple simultaneous data sources
   - Advanced UI control integration

## 🚀 Usage

1. Open `index.html` in a modern web browser
2. Use layer toggles to show/hide different visualization layers
3. Apply region filters to focus on specific continents
4. Switch metrics to view different country-level data
5. Adjust opacity sliders for optimal visual composition
6. Click countries or cities for detailed information
7. Let the globe auto-rotate or interact manually

## 📁 Project Structure

```
mapbox_globe_4/
├── index.html              # Main visualization page
├── src/
│   ├── index.js           # Multi-layer orchestration logic
│   └── data/
│       ├── countries-data.js   # 100+ countries with metrics
│       └── cities-data.js      # 80 tech hubs with connections
├── README.md              # This documentation
└── CLAUDE.md             # Development context
```

## 🎓 Key Takeaways

**Multi-Layer Mastery**:
- Successfully combined 4 different layer types (circle, line, symbol)
- Implemented coordinated visibility and opacity controls
- Created dynamic filtering across multiple data sources

**Choropleth Techniques**:
- Adapted fill layer concepts to circle-based visualization
- Implemented smooth color interpolation for data representation
- Created responsive legends that update with metric changes

**Advanced Interactivity**:
- Layer-specific controls with real-time feedback
- Cross-layer filtering maintaining data relationships
- Comprehensive popup information for both countries and cities

**Design Excellence**:
- Professional dark theme with glassmorphism effects
- Gradient-based connection visualization
- Sophisticated color schemes for multiple data dimensions

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*This iteration represents the culmination of progressive Mapbox learning, combining single-layer mastery with multi-layer composition to create a comprehensive, interactive global visualization.*