LayerChart Skill
LayerChart is a comprehensive Svelte visualization framework built on Layer Cake, providing composable components for creating responsive, interactive charts across multiple visualization types.
Core Architecture
LayerChart operates on a component-based, data-driven philosophy. The library provides three primary categories of components:
Data-Driven Components render visual marks directly from data (Area, Bars, Spline, Pie, Sunburst, Treemap, Sankey, etc.). These components automatically handle scale transformations through LayerCake's context.
Motion-Enabled SVG Primitives (Rect, Circle, Arc, Group, Line, Path) provide low-level drawing utilities with built-in Svelte transition support for animated data updates.
Utility Components handle legends, tooltips, pan/zoom interactions, annotations, and layout operations (hierarchy, geo projections).
Visualization Types
- Cartesian: Bar, Area, Stack, Scatter, Histogram, ClevelandDotPlot, BarStack, BarGroup
- Radial: Pie, Arc, Sunburst, Threshold
- Hierarchical: Pack, Tree, Treemap, Partition
- Graph: Sankey, Link, Graph utilities
- Geographic: Choropleth, Spike Map, Bubble Map, GeoTile, GeoPath, StateMap, AnimatedGlobe, Globe projections (Mercator, Azimuthal, Equal Earth, etc.)
Key Patterns
Data Preparation
Use LayerChart's data transformation utilities before passing to visualizations:
stack()- converts wide-format data into stacked series with baseline/top valuesbin()- groups data into histogram bins with x0/x1 boundsgroupLonger()- pivots wide-format to long-format (one row per value)flatten()- flattens nested arrays one level, with optional accessorcalcExtents()- calculates min/max across multiple fields, skipping nulls
Component Composition
All LayerChart visualizations sit within a LayerCake wrapper that establishes scales and context. Child components access scales via Svelte's context API.
<LayerCake x="date" y="value" data={data} padding={{...}}>
<Svg>
<Area />
<Line />
<AxisX />
</Svg>
<Canvas>
<Points /> <!-- High-performance canvas rendering -->
</Canvas>
<Html>
<Tooltip />
</Html>
</LayerCake>Interaction Patterns
- Tooltips: Position over data with snap-to-data options
- Pan/Zoom: Built-in context utilities for interactive navigation
- Highlighting: Hover states trigger visual emphasis (opacity, stroke changes)
- Selection: Use reactive variables and event handlers for interactive filtering
Responsive Design
LayerChart automatically handles responsive layouts via padding configuration and container dimensions. Components reactively update when data or scales change.
Common Implementation Tasks
Bar Charts: Use Bars component with x as categorical field. Stack with BarStack or group with BarGroup for multi-series.
Time Series: Configure xScale={scaleTime()} with temporal data. Use AxisX with tickFormat for readable date labels.
Geographic Visualizations: Select appropriate projection (Mercator for web maps, Azimuthal for polar), use GeoPath for boundaries, Choropleth for value mapping.
High-Volume Data: Render marks via Canvas instead of SVG for 5000+ points. Layer SVG axes/legends with Canvas for hybrid rendering.
Stacked/Grouped Series: Use stack() utility to transform data, then render via AreaStack/BarStack components.
Performance Considerations
- Canvas rendering for 5000+ points (~60fps on modern hardware)
- SVG for interactive elements and animations (<500 points recommended)
- Hybrid approach: Canvas for marks + SVG for axes/legends
- Scale calculations are reactive—only update scales when data/domain changes
- Memoize expensive data transforms outside component lifecycle
Styling and Customization
All primitive components support standard SVG/Canvas attributes (stroke, fill, opacity, strokeWidth). Use Svelte's reactive statements for conditional styling based on interaction state or data values.
Gradient fills, patterns, and clipping available via ClipPath, RectClipPath, CircleClipPath components with SVG <defs>.
Integration Notes
- Works seamlessly with D3 scales (linear, time, ordinal, log, threshold)
- Supports multiple render contexts in same chart (SVG + Canvas + HTML)
- Fully accessible with ARIA attributes on SVG elements
- SSR-compatible for server-side rendering in SvelteKit
- Zero external dependencies beyond Svelte and d3-array utilities