Mark

Mark = "point" | "line" | "area" | "bar" | "rect" | "arc" | "rule" | "tick" | "text" | "link" | "polygon" | "glyph"

Defined in: spec/mark.ts:9

The geometric primitive drawn once per datum.

A chart type is not a mark: a heatmap is rect with categorical position and quantitative colour, a histogram is bar with a binned position, a flamegraph is rect in hierarchical coordinates. Naming the primitive rather than the chart is what keeps the catalogue open.