Interpolation and grids

• Set property and weight on turf.interpolate so numeric sample values drive the grid.
• Pass a bbox array, not a polygon, as the first argument of turf.hexGrid.
• Choose five to ten breakpoints for turf.isolines so contour lines stay readable.

var samples = turf.featureCollection([
  turf.point([116.38, 39.90], { value: 42 }),
  turf.point([116.40, 39.91], { value: 58 }),
  turf.point([116.42, 39.89], { value: 35 }),
  turf.point([116.44, 39.92], { value: 71 })
]);

var grid = turf.interpolate(samples, 0.5, {
  gridType: 'point',        // point | square | hex
  property: 'value',
  units: 'kilometers',
  weight: 2                 // 距离的幂次，越大越「只信近处」
});

console.log(grid.features.length);
console.log(grid.features[0].properties);   // 含 value 插值结果

var lines = turf.isolines(samples, [30, 40, 50, 60, 70], {
  zProperty: 'value',
  commonProperties: { unit: 'μg/m³' }
});

lines.features.forEach(function (f) {
  console.log(f.properties.value, f.geometry.type);
});

• String-valued properties become NaN and leave the whole grid null without an error.
• Small cellSize values such as 0.1 kilometers can generate hundreds of thousands of cells and freeze the main thread.