H3 Hexagonal Grid

H3 partitions the globe into 12 base pentagons and a recursive subdivision of hexagonal cells across 16 resolution levels. Each cell is uniquely identified by a 64-bit integer index, enabling deterministic spatial referencing. The hexagonal geometry ensures uniform adjacency—every cell has six equidistant neighbors—eliminating the diagonal connectivity ambiguities inherent in square grids. Resolution ranges from 1,107 km² at level 0 to 0.9 m² at level 15, allowing spectrum maps to scale from continental overviews to micro-cell propagation analysis.

Unlike traditional geohash or S2 square grids that suffer from significant area distortion at high latitudes, H3 hexagons maintain minimal variation in cell area across the globe. The maximum area ratio between the largest and smallest cell at any given resolution is kept below 1.4x, compared to orders of magnitude for equal-angle grids. This property is critical for spectrum occupancy heatmaps, where signal power density calculations require consistent spatial binning to avoid statistical bias in aggregated RF measurements.

H3 cells serve as the canonical spatial support for geostatistical interpolation in REM construction. Kriging and Gaussian Process Regression models compute variogram parameters over H3 cell centroids, treating each hexagon as a discrete measurement support. The uniform cell area ensures that sensor density normalization—dividing aggregated signal counts by cell area—is consistent across latitudes. This enables accurate spectrum cartography where predicted power spectral density values are assigned to H3 indexes for efficient spatial querying.

H3 provides polyfill and polygonToCells functions that convert arbitrary geofences—such as exclusion zones, incumbent protection contours, or building footprints—into sets of H3 indexes at a specified resolution. This enables:

• Spectrum Access System (SAS) enforcement by pre-computing prohibited transmission cells
• Propagation coverage maps by intersecting ray-tracing output polygons with H3 grids
• 3D city model integration by mapping building geometries to H3 cells for diffraction loss lookup tables

The gridDisk and gridRing functions return the set of H3 indexes at a specified k-ring distance from a central cell. This deterministic adjacency structure makes H3 an ideal graph topology for Graph Neural Networks (GNNs) applied to REM interpolation. Sensors are represented as nodes at their H3 cell centroids, and edges connect neighboring cells. Message-passing layers propagate RF measurements across the graph, enabling spatial-temporal interpolation that respects the true geographic connectivity of the sensor network.