H3 children cells

Model: H3 v4 hierarchy (h3o 0.11): 7 children per step, 6 for pentagons

Accuracy: Identical to H3 C

When to use this: Use this when moving to a finer resolution: the cells inside a cell one or more levels down, their count, and the center child. It is how a coarse aggregation is broken into a finer one, and how a cell is refined where more detail is wanted. It is also how a coarse selection is refined for rendering: draw the parent at a distance, its children when zoomed in, which is the usual level-of-detail pattern on a hexagonal grid.

Limitations: H3's hierarchy is not an exact subdivision: children do not tile their parent exactly, so a child near the edge overlaps the neighboring parent. The count grows by about seven per level, so refining several levels at once produces very large sets; a pentagon has fewer children than a hexagon. Each level multiplies the count by roughly seven, so going three levels down from one cell is already several hundred cells and five levels is tens of thousands.

Worked example: Children of 892a8471487ffff at resolution 10. Source: add-spatial-indexing-and-raster scenario: 7 children. It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.

Review: Not yet independently reviewed by a GIS professional.

Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Changes

• 2026-09-19, changed: Eight more H3 tools are stable: the cell inspector, grid ring, grid path, parent, children, compact, uncompact, and edges. On 300 cells at every resolution, one in eight a pentagon, they match H3 C exactly, including every path H3 C refuses; cell areas agree to 2e-8 relative even at resolution 15. Results are unchanged. Changelog

Checked against: 20 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• H3: A Hexagonal Hierarchical Geospatial Indexing System (API reference v4), Uber Technologies and the H3 contributors, H3 4.x documentation. Indexing, inspection, traversal, hierarchy, directed edges, vertexes, and resolution tables. Read free.
• h3o: a Rust implementation of H3, Hydronium Labs, 0.11.0 (tested against H3 C). CellIndex, LatLng, Resolution. Read free.

Terms

H3: H3 hexagonal hierarchical index

A global grid of hexagons (and 12 pentagons) at 16 resolutions, each cell about one-seventh the area of its parent, named by a 15-character index. Source: H3 hexagonal index