Stream Graph

Source: Data Visualisation Catalogue - Stream Graph

Why This Belongs In The Compiler Gallery

Stream graphs are the natural next test after stacked area graphs. They use the same stacked area bands, but the stack baseline is centered around a moving middle instead of starting at zero. That makes the chart a focused compiler test for non-zero stack baselines plus smooth area path interpolation.

Data Contract

Each raw row represents one series value at one ordered period.

Field	Type	Purpose
`period`	ordinal	Ordered position on the x-axis.
`periodIndex`	quantitative	Stable sort key for path construction.
`series`	categorical	Stream member and color key.
`value`	quantitative	Raw magnitude.
`start`	quantitative, derived	Lower boundary emitted by the stream stack mode.
`end`	quantitative, derived	Upper boundary emitted by the stream stack mode.

Expected Visual

The faithful catalogue version should show smooth colored bands flowing across periods, with the total stack centered around a changing baseline. The chart emphasizes relative flow shape more than exact point reading.

Element	Expected treatment
Bands	Filled area bands between `start` and `end`.
Baseline	Centered per period by the stack transform's stream mode.
Curve	Smooth interpolation through ordered period centers.
Color	Ordinal palette keyed by `series`.
Legend	Generated color legend.

Compiler Mapping

Compiler part	Mapping
Data source	`raw-stream-series` and derived `segments`.
Transform	`stack` with `mode: "stream"` computes centered `start` and `end` boundaries.
Scales	`x: band`, `y: linear(start/end)`, `color: ordinal`.
Layers	Smooth `path` area bands using `y0` and `y1`.
Guides	Generated x/y axes, gridlines, and color legend.

Faithfulness Notes