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FAQ

General​

What is IGEO7?​

IGEO7 is a Discrete Global Grid System (DGGS) that partitions the entire Earth surface into a hierarchy of equal-area hexagonal cells, identified by 64-bit integer indexes called Z7 indexes. It is described in the AGILE 2025 paper.

How is IGEO7 different from H3?​

Both use hexagonal cells on an icosahedron with 64-bit hierarchical integer indexes. The key difference is projection: IGEO7 uses the ISEA equal-area projection (0% cell area variation); H3 uses the gnomonic projection (up to ±50% variation). IGEO7 also has 21 resolution levels vs H3's 16. See IGEO7 vs H3 for the full comparison.

Is IGEO7 a drop-in replacement for H3?​

Not directly — the index values are incompatible, and you need DGGRID or DGGAL instead of the H3 C library. However, the programming model is very similar: index points to cells, navigate hierarchy via parent/child, look up neighbours. Migration requires re-indexing your data, but the API concepts map closely.

What does "Z7" mean?​

Z7 refers to the hierarchical indexing system based on aperture-7 hexagonal refinement (each cell has 7 children). The "Z" reflects the space-filling Z-order / space-filling curve property of the index ordering.

Technical​

Why do IGEO7 cells have exactly 12 pentagons?​

By Euler's formula for convex polyhedra, any tiling of a sphere using hexagons requires exactly 12 pentagons. IGEO7 places these at the 12 vertices of the icosahedron — as far apart as possible and away from densely populated land. See DGGS Fundamentals.

What is CLS and why use it instead of area?​

CLS (Characteristic Length Scale) is the diameter of a circle with the same area as a cell. It's the most intuitive way to relate IGEO7 resolutions to traditional raster pixel sizes — "resolution 9 has a CLS of ~1.3 km" is more immediately useful than "1,263,990 m²". See Resolution Table.

What are the authalic latitudes and do I need to worry about them?​

DGGRID uses authalic latitudes internally to implement the ISEA equal-area projection on the WGS84 ellipsoid. You do not need to handle this — dggrid4py passes standard WGS84 lat/lng and DGGRID converts internally. It is only relevant if you are implementing the ISEA projection from scratch. See ISEA Projection.

Why does my Z7 hex index end in ffffffff?​

The f digits in a Z7 hex string represent 1111₂ = digit value 7, which is the sentinel meaning "beyond resolution". A hex index like 0042aad3ffffffff has 9 valid digits (resolution 9) followed by 11 sentinel groups. This is normal and expected. See Z7 Bit Layout.

Can I store Z7 indexes in PostgreSQL / DuckDB / BigQuery?​

Yes. Store as:

  • BIGINT (PostgreSQL), INT8 (DuckDB), INT64 (BigQuery) for the integer
  • VARCHAR(22) for the Z7 string
  • CHAR(16) for the hex string

The Z7 string's prefix property makes hierarchical queries efficient with a standard B-tree index:

-- All resolution-9 descendants of resolution-5 cell "0800433"
SELECT * FROM observations WHERE cell_id LIKE '0800433%';

Tooling​

Do I need DGGRID installed to use IGEO7?​

For coordinate → cell conversion and grid generation, yes — dggrid4py requires the DGGRID binary. For index arithmetic (resolution, parent, children, format conversions), the dggrid4py.igeo7 module is pure Python with no DGGRID dependency.

Alternatively, DGGAL (pip install dggal) implements the full IGEO7 stack natively in C++ with no subprocess overhead.

Is there a JavaScript / web implementation?​

Not yet. A WebGPU/Deck.gl integration is on the roadmap. GeoPlegma is developing JavaScript and native Rust support.

Can I use IGEO7 with QGIS?​

Yes — generate cell polygons with dggrid4py (as GeoPackage or GeoJSON) and load them in QGIS like any vector layer. Native QGIS plugin support is not yet available.

Is there an R binding?​

Not officially. The DGGRID binary can be called from R via system(), and there are community packages wrapping DGGRID for R (e.g. dggridR), though these target other grid types. Z7 index arithmetic can be ported to R straightforwardly from the Python or Julia implementations.

Licensing​

What licence is IGEO7 / DGGRID under?​

DGGRID is licensed under the AGPL-3.0. dggrid4py and pydggsapi are also AGPL-3.0. IGEO7.jl is MIT. The IGEO7 index specification itself is open and unencumbered.