Driver brief §B, the seam under the language tree, so gospel's set charts inherit zoom,
label priority and tiling from the map engine instead of re-implementing them in SVG.
READ FROM GiTree RATHER THAN ASSUMED: six layer groups, exactly ONE hierarchical. The
parent->child links are sourced from linkFC; the points, the selection and hover rings,
the dish behind a cluster and EVERY label layer come from one point collection and know
nothing about trees. gospel re-read that independently and found the same split, which
is the only reason I trust it -- "the seam is generic" is the claim that should never
travel on one reader.
So library/charts/whiteboard/tiered-points.js takes a point FeatureCollection whose
features carry id, label, tier and priority, and gives each TIER its own symbol layer
with its own minzoom. That is the whole of "band names zoomed out, ring names mid, group
names in": the engine is told which labels may exist at which zoom and resolves the
collisions itself. Paint expressions pass through unread -- the layer has no opinion
about what a colour means, which is what keeps it reusable. Selection and hover are
FILTERED layers, so hover costs one setFilter and structurally cannot move a camera:
there is nothing in here that could.
AND THE PROJECTION IS NOT A SCALE, which is the part that would have shipped wrong.
gospel asked for degrees and planned to scale by one number; their charts are CONCENTRIC
RINGS, and Mercator stretches vertically by 1/cos(lat) -- 1.0154x at 10 degrees, 1.1547x
at 30 -- so a linear scale renders rings as OVALS, worst at the outer ring where the
labels a reader compares are. library/maps/whiteboard-projection.js is the inverse
conversion, EXTRACTED from build-language-tree.mjs rather than written, because the
second copy was about to be made by hand. The degree-height it emits shrinks from 0.9996
of the width at the centre to 0.6794 at the edge; that shrink IS the correction the
renderer then cancels.
TWO TESTS, EACH GUARDING A DIFFERENT RISK.
check:whiteboard-projection reproduces the old private implementation VERBATIM as a
reference and compares over 1,734 grid points EXACTLY -- the language tree is a
build-time artifact, so a rounding shift would move 4,000 coordinates and look like
nothing. It then asserts a ring renders round at the inner, middle and outer radii, AND
that a linear scale FAILS that same assertion, because an assertion the defect can pass
is measuring nothing.
check:tiered-points runs gospel's CENTERED SET through the layer: 2,079 points, 3 tiers,
priority by population, and NO EDGES. The absent links layer is the evidence -- if the
whiteboard draws this chart with no line layer anywhere, edges are separable in fact
rather than in my reading. The map is a recording fake, so the assertions are about what
the module DOES; a regex over the source would pass on a module that never called
addLayer.
Negative-tested: making the projection linear, changing its rounding, dropping the label
priority, or giving every tier the same minzoom each turn one of them red.
gospel's UI is NOT wired -- their component is theirs to write, later, against a module
that now exists. Their boardEngine.js stays where it is until the chart lands.
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