Marks

A mark is the visual primitive that data rows become — bars, lines, arcs, etc. Specify via top-level mark (shorthand string) or mark: {type: "...", ...properties}.

Catalog

Basic marks (Vega-Lite parity)

Mark	When to use
`bar`	Compare categories. The default.
`line`	Continuous trends; ordered x-axis.
`area`	Filled trends. Supports negative values + stacks.
`point`	Scatter, dot plots.
`circle`, `square`	Convenience aliases for `point` with shape preset.
`tick`	Strip plots, ranking dot plots.
`rect`	Heatmap cells, custom rectangular layouts.
`rule`	Reference lines, benchmarks, ranges.
`text`	Inline labels, annotations.
`arc`	Primitive for `pie` / `donut` / sankey links.

Composite marks

Mark	Internally expands to
`histogram`	`bar` + auto-bin transform.
`heatmap`	`rect` + 2D bin + sequential color scale.
`boxplot`	`rect` (IQR) + `rule` (whiskers) + `point` (outliers).
`violin`	`area` symmetric around centerline (Epanechnikov KDE).
`pie`	`arc` with theta computed from share.
`donut`	`arc` with `inner_radius_ratio > 0`.

Specialty marks

Mark	When to use
`sankey`	Flow diagrams (source/target/value table).
`funnel`	Conversion funnels — stacked trapezoids.
`sparkline`	Inline micro-line charts, no axes.
`image`	Sprites / data-URL images at position.
`path`	Raw SVG path data — escape hatch.
`geoshape`	Country / admin-1 polygons (choropleth). See Geographic Marks.
`geopoint`	Lon/lat → point overlay. See Geographic Marks.

Hierarchical and relational marks share a small layout package (encode/marks/layout) and decompose to existing primitives (path, point, rect, text) so the SVG and PDF renderers handle them without new geometry types.

Mark	When to use
`tree`	Rooted hierarchy (org charts, decision trees). Reingold-Tilford tidy layout.
`dendrogram`	Clustering tree — tree variant with `link_shape: step` + `node_shape: none` defaults.
`network`	Undirected / directed node-link diagram. Force-directed layout (deterministic seed).

Channel bindings:

source — parent / from-node id field (required for tree/dendrogram/network).
target — child / to-node id field (required).
value — optional edge weight (network) / node size (tree).
text — optional per-node label.
color, fill, stroke, opacity, size — standard mark props.

Mark-def options:

orient — vertical (default), horizontal, radial.
link_shape — step (default), curve, straight.
node_shape — circle (default), rect, none.
node_size — base radius / side length (default 6).
layout (network) — force (default), random.
iterations, link_distance, charge, seed (network).

Validate rules: PRISM_SPEC_028 (missing source/target), PRISM_SPEC_029 (multi-root tree). Encode-time: PRISM_ENCODE_TREE_CYCLE, PRISM_ENCODE_NETWORK_NONFINITE, PRISM_WARN_NETWORK_CYCLE.

Channel allowlists

Not every channel is valid for every mark — theta only makes sense on arc, source/target only on sankey, etc. The validator catches mismatches with PRISM_SPEC_003.

Worked examples

Every mark above has a fixture in the gallery. Start with:

Prism Documentation