Road width does not change with zoom

• The same road measures 3 screen pixels at both zoom 12 and zoom 17
• `156543.03392 / 2**12` is 38.22 m per pixel versus `1.19` m per pixel at z17
• Raising `weight` to 12 makes roads a solid band at zoom 12 that covers whole blocks

1. Screenshot the same road at two zoom levels and measure its pixel width
2. Check whether `weight` is hardcoded in the style function
3. Check for a `zoomend` handler that resets weight and inspect its formula
4. Compare against the basemap road width to set a target ratio
5. Compute metres per pixel at each zoom level

Interpolate width in Mapbox GL (`'line-width': ['interpolate', ['exponential', 1.5], ['zoom'], 8, 0.8, 12, 1.6, 16, 4, 18, 7]`), or recompute `weight` on `zoomend` in Leaflet with a stepped function returning 1 below z10 up to 5 above z16.

17 级：156543.03 / 2^17 ≈ 1.19 米/像素
12 级：156543.03 / 2^12 ≈ 38.22 米/像素

console.log(156543.03392 / Math.pow(2, 12));   // 38.22
console.log(156543.03392 / Math.pow(2, 17));   // 1.19

• Setting one large `weight` so high zooms look right, which turns roads into solid bands at low zoom
• Calling `setStyle` on `zoomend` without a style function, which resets every other style property