Population Pyramid

Source: Data Visualisation Catalogue - Population Pyramid

Why This Belongs In The Compiler Gallery

The catalogue population pyramid is a practical test for diverging bar charts. It needs ordinary rect marks, but it also needs compiler-owned signed geometry so left and right cohorts share one symmetric scale and one zero spine.

Data Contract

Each raw row represents one age cohort with two positive measures.

Field	Type	Purpose
`ageGroup`	ordinal	Cohort label shown on the y axis.
`male`	quantitative	Left-side population measure.
`female`	quantitative	Right-side population measure.
`side`	categorical, derived	Output side label.
`value`	quantitative, derived	Positive cohort value.
`signedValue`	quantitative, derived	Negative left value or positive right value for symmetric domains.
`start`	quantitative, derived	Rect start bound on the diverging x scale.
`end`	quantitative, derived	Rect end bound on the diverging x scale.

Expected Visual

The faithful catalogue version should show two mirrored horizontal bars for every age cohort. Left and right bars meet at a shared zero centerline, and x-axis labels should read as absolute values instead of negative values on the left.

Element	Expected treatment
Cohort bars	Rects using `start` and `end` bounds from the diverging layout transform.
Centerline	Vertical guide line at zero.
X axis	Symmetric quantitative scale with absolute tick labels.
Y axis	Age cohort labels in input order.
Color	Side-based categorical encoding.

Compiler Mapping

Compiler part	Mapping
Data source	`age-population` raw cohort table and derived `pyramid-segments` table.
Transform	`layout` with `layoutKind: "divergingBars"` derives left/right segment rows.
Scales	`x: linear` with `symmetric` and `padding`, `y: band`, `color: ordinal`.
Guides	Generated x grid/axis, generated y labels, generated side legend, and an explicit zero centerline.
Layers	Rect bars plus guide layers.
Interaction	Hover exposes age cohort, side, value, and source row.

Faithfulness Notes