Contour · Low-resolution grid
49 samples produce straight segments within each cell. A denser source grid provides more detail.
Use isolines to compare equal scalar values across a numeric field. Line spacing follows the original coordinate grid; it does not imply a geographic projection.
grid.x and grid.y contain increasing numeric coordinates. grid.values and grid.ids are row-major original measurements, with null for unknown values. Isolines are derived using marching squares with bilinear saddle decisions; tooltips distinguish their requested level from the four original corner measurements.
A 2–64 by 2–64 grid, up to 4096 original samples and 1–8 strictly increasing levels. layout.levels contains only{id,value}; names and colours use appearance.series with the same IDs. The default 4096 segment budget can be increased to 8192. Exceeding it returns a diagnostic, never incomplete geometry. Filled contours, smoothing, markers, stacking and shared tooltips are unavailable.