Thanks for your help. The resulting number has 12 digits :-) I narrowed the calculation load down with this query, it gives me an empty result even though there should be some hexagons: SELECT h3_polygon_to_cells(polygon(poly.way), array[]::polygon[], 8) FROM planet_osm_polygon poly WHERE admin_level = '8' AND name = 'Jever' Admin level 8 is municipality level and Jever is big enough to have some hexagons of resolution 8 in it. Anyway, for my purpose that computation is way too slow, I guess I need to do it with application code. But would be nice to see the function working.

You're right, I got a logical error in my thinking there - I thought limiting the results to a low number will increase speed, but thats nonsense because the area to be calculated is massive.