| name | h3-pg |
| description | PostgreSQL bindings for H3 hexagonal grid system. Use when working with H3 cells in Postgres, including spatial indexing, geometry/geography integration, and raster analysis. |
h3-pg PostgreSQL Extension
Extension Architecture
Two extensions:
CREATE EXTENSION h3 — Core H3 bindings (indexing, traversal, hierarchy, inspection, <-> operator). No PostGIS dependency.CREATE EXTENSION h3_postgis — PostGIS integration (geometry/geography casts, @ operator, polygon fill, raster helpers). Requires postgis and optionally postgis_raster.
Postgres-Specific H3 Features
These exist only in h3-pg, not other H3 language bindings.
Direct casts (h3_postgis):
h3index::geometry → cell centroid as POINT, SRID 4326h3index::geography → cell centroid as POINT, SRID 4326
Operators:
a <-> b — grid distance in cells between two h3index values (h3)geom @ resolution — index geometry/geography at resolution (h3_postgis)
Inspection and construction helpers (h3):
h3_get_index_digit(cell, resolution) — inspect the digit at a 1-based resolution steph3_construct_cell(resolution, base_cell_number, digits[]) — rebuild a cell from explicit componentsh3_is_valid_index(index) — validate any H3 index mode: cell, directed edge, or vertex
Directed edge convenience (h3):
h3_reverse_directed_edge(edge) — returns the same directed edge with origin and destination reversed
Operator classes for h3index: BTREE, HASH, BRIN, SP-GIST (h3)
Boundary helpers (h3_postgis):
h3_cell_to_boundary_geometry(h3index) → polygon with SRID 4326, splits at antimeridianh3_cell_to_boundary_geography(h3index) → geography polygon, splits at antimeridian
Polygon fill (h3_postgis):
h3_polygon_to_cells(geometry, resolution) → SETOF h3indexh3_polygon_to_cells(geography, resolution) → SETOF h3index
Raster integration (h3_postgis, requires postgis_raster):
h3_raster_summary(raster, resolution, [band]) — per-cell stats (count, sum, mean, stddev, min, max)h3_raster_summary_clip(...) — clips raster by cell boundariesh3_raster_summary_centroids(...) — uses cell centroids, avoids pentagon edge casesh3_raster_summary_subpixel(...) — for cells smaller than pixelsh3_raster_class_summary*(...) — discrete class counts per cell
Tile helper (h3_postgis):
h3_get_resolution_from_tile_zoom(z, [max_h3_resolution=15], [min_h3_resolution], [hex_edge_pixels=44], [tile_size=512]) — returns optimal H3 resolution for XYZ tile zoom level z, targeting hexagons approximately hex_edge_pixels wide on screen
Common Pattern Fixes
| Pattern | DO NOT | DO |
|---|
| Get centroid | ST_Centroid(h3_cell_to_boundary_geometry(h3)) | h3::geometry |
| Get boundary with SRID | h3_cell_to_boundary(h3)::geometry | h3_cell_to_boundary_geometry(h3) |
| Distance check (meters) | ST_Distance(a.h3::geography, b.h3::geography) <= N | ST_DWithin(a.h3::geography, b.h3::geography, N) |
| Grid distance (cells) | h3_distance(a, b) | a <-> b |
Antimeridian gotcha: Cells crossing 180° are split into valid polygons. ST_Centroid of a split polygon may fall outside the cell — use h3::geometry for centroids instead.
Ring traversal gotcha: Prefer h3_grid_ring(origin, k) for rings because it handles pentagon distortion internally. Use h3_grid_ring_unsafe(origin, k) only when fail-fast behavior or ring-walk ordering matters.
Critical v3 → v4 Renames
| v3 Name (DO NOT USE) | v4 Replacement |
|---|
h3_geo_to_h3 | h3_latlng_to_cell |
h3_to_geo | h3_cell_to_latlng |
h3_to_geo_boundary | h3_cell_to_boundary |
h3_k_ring | h3_grid_disk |
h3_k_ring_distances | h3_grid_disk_distances |
h3_hex_ring | h3_grid_ring_unsafe |
h3_line | h3_grid_path_cells |
h3_distance | h3_grid_distance |
h3_to_parent | h3_cell_to_parent |
h3_to_children | h3_cell_to_children |
h3_compact | h3_compact_cells |
h3_uncompact | h3_uncompact_cells |
h3_polyfill | h3_polygon_to_cells |
h3_indexes_are_neighbors | h3_are_neighbor_cells |
h3_hex_area | h3_get_hexagon_area_avg |
h3_hex_area_km2 / h3_hex_area_m2 | h3_get_hexagon_area_avg(res, unit) |
h3_edge_length_km / h3_edge_length_m | h3_get_hexagon_edge_length_avg(res, unit) |
Unit parameters (v4): Area and length functions now take a unit text parameter:
h3_get_hexagon_area_avg(resolution, [unit = 'km^2']) — use 'km^2' or 'm^2'h3_get_hexagon_edge_length_avg(resolution, [unit = 'km']) — use 'km' or 'm'h3_cell_area(cell, [unit = 'km^2']) — exact area for specific cellh3_edge_length(edge, [unit = 'km']) — exact length for specific edge
Spelling change (v4.2.3+): Prefer h3_latlng_to_cell over h3_lat_lng_to_cell (underscore version deprecated). Same for h3_cell_to_latlng, h3_vertex_to_latlng.
Documentation
