COMPARING AREA AND SHAPE DISTORTION ON POLYHEDRAL-BASED RECURSIVE PARTITIONS OF THE SPHERE

Regular grid sampling structures in the plane are a common spatial fra mework for many studies. Constructing grids with desirable properties such as equality of area and shape is more difficult on a sphere. We s tudied the distortion characteristics of recursive partitions of the s urface of the globe starting with the octahedron and icosahedron polyh edral models. We used five different methods for mapping from the poly hedral model to the surface of the sphere: the Gnomonic projection, Fu ller's Dymaxion projection, Snyder's equal area polyhedral projection, direct spherical subdivision, and a recursive polyhedral projection. We increased partition density using both a cl-fold and a 9-fold ratio at each level of recursive subdivision by subdividing to the 8th leve l with the 4-fold density ratio (65 536 cells per polyhedral face) and to the fifth level with the 9-fold density ratio (59 049 cells per po lyhedral face). We measured the area and perimeter of each cell at eac h level of recursion for each method on each model using each density ratio. From these basic measurements we calculated the range and stand ard deviation of the area measurement, and the mean, range, and standa rd deviation of a compactness measurement defined as the ratio of(the ratio of the perimeter to the area of the cell) to (the ratio of the p erimeter to the area of a spherical circle with the same area). We loo ked at these basic measurements and their statistics using graphs of v ariation with recursion level, sums of squares analyses of variation, histograms of the distributions, maps of the spatial variation, and co rrelograms. The Snyder projection performed best in area distortion an d the Gnomonic projection performed best in compactness distortion. Th e Fuller projection and the Sphere method had moderate distortion in b oth area and compactness relative to the worst methods. There was litt le difference in distortion performance between partitions using the 4 -fold density ratio and those using the 9-fold density ratio. Partitio ns based on the icosahedron performed better for all statistics than t hose based on the octahedron.