IGEO7: A new hierarchically indexed hexagonal equal-area discrete global grid system

Abstract. Hexagonal Discrete Global Grid Systems (DGGS) offer significant advantages for spatial analysis due to their uniform cell shapes and efficient indexing. Among the three central place apertures (3, 4, and 7), aperture 7 subdivisions exhibit very desirable properties, including the preservation of hexagonal symmetry and the formation of unambiguous indexing hierarchies. Interest in hierarchically indexed aperture 7 hexagonal DGGS has recently increased due to the popularity of the H3 DGGS. But there are currently no open-source equal-area aperture 7 hexagonal DGGS available, that provide similar indexing capabilities like H3. We present IGEO7, a novel pure aperture 7 hexagonal DGGS, and Z7, its associated hierarchical integer indexing system. In contrast to H3, where cell sizes vary by up to ±50% across the globe, IGEO7 uses cells of equal area, making it a true equal-area DGGS. IGEO7 and Z7 are implemented in the open-source software DGGRID. We also present a use case for on-demand suitability modeling to demonstrate a practical application of this new DGGS.