Rule
A scalar Channel may deliver immutable contour geometry beside its numeric tiles. contour_prefix addresses per-band GeoJSON LineStrings; each feature carries its physical value. Contours are a derived presentation of the same data, not another Provider or independently selected Channel.
The Layer owns contour visibility, color, width, opacity and dash pattern through the shared line presentation constructor in Lines. Legacy rasterContours color and width seed that presentation without restyling existing maps; its label visibility remains independent. Conditional styles evaluate the contour value. Its numeric raster opacity remains independent, allowing lines without a colored background. Mapbox native line and symbol layers project the geometry on globe and Mercator, including the zoom 5–6 transition. Before creating the render source, contours use the same polarClip line clipping as other vector lines at ±85.05112878°. Crossings are interpolated and split; fully polar parts are omitted, without pinning them to the boundary. Both line strokes and labels consume that clipped geometry. Primary colors remain fixed; label halos use the shared basemap theme contrast rule, dark on dark basemaps and light on light basemaps.
Inspection
Hover and Details sample the declared scalar tile encoding at the chosen band, including positions between lines. Geometry is never used to infer the value between contours. The existing immutable frame cache serves further pointer positions, as described by raster pixel inspection.
Forecast consistency
The weather publisher prepares all numeric tiles and the contour file before one fenced database transaction activates the band. Changing the time removes old contour geometry and cancels its request. Style reloads restore the current native layers. Layer removal releases both representations.
Mean sea level pressure
NOAA GFS PRMSL represents pressure reduced to mean sea level, not surface pressure at terrain height. The acquisition converts Pa to hPa. RG16 tiles encode 870–1085 hPa; values outside that range are rejected during publication rather than silently represented as boundary values. Isobars use a 0.5° derived grid and a 4 hPa interval; numeric hover uses the 0.25° source sampled into the published z0–z2 pyramid. They describe modeled values at the displayed valid time, not a local barometer measurement. Contours are cut at ±180° to avoid false segments spanning the dateline.