Interpolation over Large Distances Using Spherekit

Spherekit is a spatial interpolation toolkit developed and distributed over the internet by the National Center for Geographic Information and Analysis (NCGIA). A unique feature of the software is its ability to work directly with the spherical geometry of the earth. Thus, distances, areas, and directions are spherically based, and interpolation can be carried out over large distances without distortions induced by the use of planar projections. The user can select from several interpolation methods that have been adapted to the sphere. The package also features "smart interpolation" capabilities to incorporate knowledge of the underlying physical processes that produced some of the spatial variability. Error analysis using cross-validation is built-in to compare the relative performance of interpolation algorithms or parameter settings. The cross-validation errors can themselves be interpolated to a uniform grid to reduce spatial bias. The capabilities of Spherekit are demonstrated using three examples. OVERVIEW Spherekit is a spatial interpolation software toolkit developed at NCGIA as part of Initiative 15 (Multiple Roles of GIS in Global Change Research). The source code is available over the internet without charge to the user. The package features several unique capabilities. Spherekit permits interpolation over continental or global scales because its computations are based upon spherical distances and orientations (Raskin, 1994). Conventional interpolations (Watson, 1992) are based upon planar projections of the earth that produce distortions of some kind over large distances. In Spherekit, projections are applied only for display purposes after