Spherekit is a spatial interpolation software toolkit developed at NCGIA as part of Initiative 15: Multiple Roles of GIS in U.S. Global Change Research. This package features several unique capabilities and is freely distributed over the internet. Spherekit allows interpolation over continental or global scales by computing distances and orientations (among data and interpolation points) from geodesics on the surface of the globe. Conventional interpolations typically are based upon Euclidean distance in Cartesian 2-space which involve planar projections that produce distortions of some kind. In Spherekit, projections are applied only for display purposes after the interpolation has been carried out using spherical geometry. Users can select from several interpolation algorithms that have been adapted to the sphere: inverse distance weighting, thin plate splines, multiquadrics, triangulation, and kriging. Spherekit enables the user to incorporate knowledge or information about the processes that produce the underlying spatial variations into the interpolation model. A built-in equation editor and a collection of nonlinear transforms allow the user to create and experiment with new, physically meaningful variables from the independent and dependent variables available. 

This report is a reference guide to the software and is not intended to be read from cover to cover. Chapter 2 presents four examples of the use of the software. Chapter 3 takes a single example and presents the steps required to carry out an interpolation. Chapter 4 describes each of the menu options available in Spherekit. Chapter 5 provides a technical description of the interpolation algorithms. Finally, Chapter 6 describes the download and installation procedures.