I am trying to create a map out of a file with millions of points. To make this tractable, I am using h3 to aggregate the points. After doing the aggregation using a combination of h3 and pandas in Python (adapted from here), I am converting the h3 indexes to polygon boundaries:

agg1=gdf.groupby(['h3', 'product', 'year']).agg(Total_Count=('product', 'sum')).groupby(level=0).apply(lambda x: 100*x / x.sum()).reset_index()

def add_geometry(row):
    points = h3.h3_to_geo_boundary(
      row['h3'], True)
    return Polygon(points)

agg1['geometry'] = agg1.apply(add_geometry, axis=1)

gdf_op = gpd.GeoDataFrame(agg1, crs='EPSG:4326')
output_filename = 'gridcounts.gpkg'
gdf_op.to_file(driver='GPKG', filename=output_filename)

However, when I open the file in QGIS, some hexagons are streaking across the map: enter image description here

I have a feeling it is because h3 is defined on a globe and as a result the polygons towards the edges translate to coordinate bounds which are at the opposite ends of the projected map. Does anyone have a solution to this apart from deleting the problem hexagons?


2 Answers 2


It is a projection issue. The hexagon shape is being split at the antimeridian (180 degrees). Try converting your output to a 3D coordinate system and plot in an orographic view. That should do it!


An alternative would be to represent your H3 cells as points, rather than as hexagons. That is, use h3_to_geo rather than h3_to_geo_boundary. Points won't be stretched across the antimeridian like this.

A further option is to drop the affected cells, and draw two maps each with a different central meridian.

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