Misaligned polygons, not perfect hexagons. Some pentagons. Catering for projection

Hi,

Im trying to incorprate your library on a number of solutions which require realtime translations between hex ids and geojson multi/polygons.

h3.h3SetToMultiPolygon(["85291a6ffffffff"],true)

returns

[[[[-121.87310260648961,36.48355301296484],[-121.82059177712684,36.56646154014561],[-121.88144909358076,36.64149027277887],[-121.99481876336013,36.63355254199253],[-122.0471691328904,36.550641568925464],[-121.98631059624982,36.4756707384872],[-121.87310260648961,36.48355301296484]]]]

No problem with that. The issue however is displaying this now results in an askew/misrepresented polygon on a map.

The map is in EPSG:4326. Geojson.io

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "color": "blue"
      },
      "geometry": {
        "type": "MultiPolygon",
        "coordinates": [
          [
            [
              [
                -121.87310260648961,
                36.48355301296484
              ],
              [
                -121.82059177712684,
                36.56646154014561
              ],
              [
                -121.88144909358076,
                36.64149027277887
              ],
              [
                -121.99481876336013,
                36.63355254199253
              ],
              [
                -122.0471691328904,
                36.550641568925464
              ],
              [
                -121.98631059624982,
                36.4756707384872
              ],
              [
                -121.87310260648961,
                36.48355301296484
              ]
            ]
          ]
        ]
      }
    }
  ]
}

Is this correct?

[nrabinowitz]

This appears to be working as expected. In order to divide the world into stable cells that have low shape and area distortion, the H3 grid doesn’t work like a screen-based or local hex binning algorithm with screen-aligned hexagons.

Key issues to be aware of:

• The alignment of the cells will change in different parts of the world.
• Particularly at coarse resolutions, hexagons may appear distorted at northern or southern latitudes when shown on a Mercator projection (as in web maps). This is a function of the projection, not the H3 system.
• H3 cells are not exactly equal size or equal area, though they have low shape and area distortion.
• There are 12 pentagon-shaped cells at every resolution. These are centered in water, and can be ignored for many use cases.
• Some cells (on the edges of the icosahedron used to create the grid) are subject to distortion, which adds additional vertexes on one or two edges. Hexagon cells (in the topological sense, with 6 neighbors) may have up to eight vertices, and pentagon cells may have 10.

[curran]

Amazing! Thank you so much 🙏