H3 uncompact

Model: H3 v4 uncompactCells (h3o 0.11)

Accuracy: Identical to H3 C

When to use this: Use this to flatten a mixed-resolution set back to one resolution, which is what most joins, counts, and exports need: give the set and the resolution and it returns every cell at that level covering the same area. It is the other half of compaction: data is stored or transmitted compacted, then expanded to a single resolution for joining, counting, or rendering, because most consumers assume one cell size.

Limitations: Expanding is where a compacted set becomes large: each level multiplies the count by about seven, so uncompacting a coarse set to a fine resolution can produce millions of cells. The target resolution has to be at least as fine as the finest cell in the set. Expansion is exact in area but not in count: cells that were coarse become many, and the memory and join cost follow. Uncompacting to a resolution finer than needed is the usual cause of a query that will not finish.

Worked example: 892a8471487ffff to resolution 10. Source: H3 uncompactCells. 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