What is H3, and why use it for geofences?

Last reviewed 20 October 2026

H3 is an open grid that divides the earth into hexagonal cells at sixteen resolutions, from continent-sized to under a square metre, and a geofence built from H3 cells is fast to test and easy to sign, because the question becomes whether a cell ID is in a list.

The grid

H3 is open source. Every point on earth falls in exactly one cell at each resolution, and each cell has an ID. Resolutions run from 0, with cells averaging about 4.4 million km², to 15, at under a square metre (H3 resolution table). Coarse cells contain finer ones, so a region can mix large cells in its interior with small ones along its edge.

Why hexagons

• All six neighbours of a hexagon are the same distance from its centre, which keeps distance and adjacency simple.
• Cells are compact to store and quick to compare.

Why it suits signed geofences

Testing a point against a free-form polygon means geometry at request time. Testing it against a set of H3 cells means looking up an ID. Octet accepts custom polygons only as H3 cell sets for this reason: you quantise the shape once, ahead of time, and the device compares cell IDs. The claimed cells are part of the signed proof, so a verifier can see exactly what region was tested (regions documentation).

You convert the shape to cells once. Every check after that is a lookup.

Things to watch

• Edges. Cells do not follow a boundary exactly. Choose a finer resolution along the edge, and decide whether edge cells count as inside or outside.
• Size. Very fine cells over a large area make long lists. Mix resolutions.