A comparison of intercell metrics on discrete global grid system Matthew J. Gregory a, * , A. Jon Kimerling b , Denis White c , Kevin Sahr d a Department of Forest Science, Oregon State University, Corvallis, OR 97331, USA b Department of Geography, Oregon State University, Corvallis, OR 97331, USA c US Environmental Protection Agency, Corvallis, OR 97331, USA d Department of Computer Science, Southern Oregon University, Ashland, OR 97520, USA Abstract A discrete global grid system (DGGS) is a spatial data model that aids in global research by serving as a framework for en modeling, monitoring and sampling across the earth at multiple spatial scales. Topological and geometric criteria have been evaluate and compare DGGSs; two of which, intercell distance and the ‘‘cell wall midpoint” criterion, form the basis of this st propose evaluation metrics for these two criteria and present numerical results from these measures for several DGGSs. We the impact of different design choices on these metrics, such as predominant tessellating shape, base modeling solid and pa between recursive subdivisions. For the intercell distance metric, the Fuller–Gray DGGS performs best, while the Equal Angle DGGS performs substantially For the cell wall midpoint metric, however, the Equal Angle DGGS has the lowest overall distortion with the Snyder and Fulle DGGSs also performing relatively well. Aggregation of triangles into hexagons has little impact on intercell distance measurements, although dual hexagon aggregation results in markedly different statistics and spatial patterns for the cell wall midpoint property. In all cases, partitions on the icosahedron outperform similar partitions on the octahedron. Partition density accounts for little v Ó 2007 Elsevier Ltd. All rights reserved. Keywords:Discrete global grid system; Intercell distance; Cell wall midpoint; Goodchild criteria; Distortion analysis 1. Introduction In recentyears,the development of globalanalytical methods, data collection instruments and increased atten- tion on global science issues have combined to spur growth in global dynamicmodeling applications. Atmospheric motion, meta-population simulations, and coupled cli- mate-vegetation models are just a few examples of dynamic systems studied using a global context ( Heikes & Randall, 1995a; Murray, 1967; Neilson & Running, 1996). Many of these applications rely on data structures that partition the globe into areal cells and associated cell centers, which we refer to as discrete global grid systems (DGGSs) (Sahr, White, & Kimerling, 2003). Movement between cells is an important function in these dynamic systems and simulate motion may be confounded by underlying distortion in the DGGS being used. A DGGS ideally would have cell cen- ters equidistant from one another and maximally central within the areal cell,which would ensure that movement from a cell to any of its neighbors is equally probable. To this end,there is growing interest in creating DGGSs that exhibit high geometric regularity among the cells and associated point lattices across the entire globe ( Heikes & Randall, 1995a; White, Kimerling, & Overton, 1992 ). Total geometric regularity (simultaneous equivalence of shape,surface area and intercell distance)can only be achieved on the spherical models of the five Platonic solids (Sahr et al., 2003) (Fig. 1). Any subsequent partitioning of these (or any other) spherical models necessarily introduce 0198-9715/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.compenvurbsys.2007.11.003 * Corresponding author. Tel.: +1 541 758 7778; fax: +1 541 758 7760. E-mail addresses: matt.gregory@oregonstate.edu (M.J. Gregory), kimerlia@geo.oregonstate.edu (A.J. Kimerling), white.denis@epamail. epa.gov (D. White), sahrk@sou.edu (K. Sahr). www.elsevier.com/locate/compenvurbsys Available online at www.sciencedirect.com Computers, Environment and Urban Systems 32 (2008) 188–203