Changing CRS to EPSG:4326 squashes the map vertically

• After setting crs: L.CRS.EPSG4326, a 1 km circular buffer measures about 1.30 wide-to-high on screen.
• A 10 km north-south road near Beijing at 39.9 N is only 76.7% as long on screen as under EPSG:3857.
• Provincial boundaries look horizontally stretched and the country outline appears flattened.

1. Draw a known 1 km x 1 km square and measure its on-screen width and height.
2. Print map.options.crs.code to confirm whether the map is on EPSG:4326 or EPSG:3857.
3. In a moveend handler compare map.getSize() with map.getBounds() and compute pixels-per-degree in both directions.
4. Switch back to the default CRS and measure again; a restored shape confirms the projection choice is the cause.

Keep the default EPSG:3857 for display; use EPSG:4326 only for equal-angle gridded data such as weather rasters, and never for vector data that must keep its shape.

map.on('moveend', () => {
  const b = map.getBounds(), s = map.getSize();
  const pxPerLon = s.x / (b.getEast() - b.getWest());
  const pxPerLat = s.y / (b.getNorth() - b.getSouth());
  console.log('px/度 经:', pxPerLon.toFixed(3), '纬:', pxPerLat.toFixed(3));
});

const map = L.map('map', { center: [39.909, 116.397], zoom: 10 });
const map4326 = L.map('map2', {
  crs: L.CRS.EPSG4326,
  center: [39.909, 116.397],
  zoom: 5
});
L.tileLayer('https://example.com/4326/{z}/{y}/{x}.png', {
  tileSize: 256,
  noWrap: true,
  bounds: [[-90, -180], [90, 180]]
}).addTo(map4326);

• Changing the CRS to 'get degrees straight out of the API'; Leaflet still works in projected pixels internally.
• Building 4326 tile layers without adjusting tileSize and bounds, which yields misaligned or half-empty tiles.