# Icosahedral Snyder Equal Area Aperture 3 Hexagonal Grid

Also known as ISEA3H, a popular type of Geodesic Discrete Global Grid System.

In biodiversity science, local discrete grids are staked out in field studies to ensure appropriate statistical sampling. Larger multi use grids are deployed at regional and national levels to develop an aggregated understanding of biodiversity. These regional grids translate environmental and ecological monitoring data from multiple spatial and temporal scales into assessments of current ecological condition and forecasts of risks to our natural resources. With global analysis it therefore seemed a natural next step to develop a global grid that would allow all ecologically significant information to be located and indexed at its own level of granularity. This was the general goal of Denis White of the US-EPA in 1990, when he identified a need for an optimized global grid to support of EPA’s Environmental Monitoring and Assessment Program (EMAP) and concluded that a statistically appropriate grid did not exist.

Subsequently, a program of research was set up in collaboration with Jon Kimerling and Scott (WS) Overton at Oregon State University. Criteria for an optimized global grid were developed spawning the evaluation and development of several approaches using regular tiling’s of square, triangular and hexagonal cells for discrete Earth partitioning. John Snyder contributed a methodology to meet the group’s primary requirements – partitioning areas equal in size over the entire globe. Other criteria for an optimized global grid were assembled and a conclusion was made in 1998 (revisited in 2003) that presented a global partitioning using a recursion of an aperture (base) 3 hexagonal grid also known as a square root three subdivision. The discrete grid was to be projected from the face of an Icosahedron to a sphere using Snyder’s equal area projection. The technique became known as the Icosahedral Snyder Equal Area aperture 3 Hexagonal (ISEA3H) grid, the basis for an optimized geodesic Discrete Global Grid System.