Keith C. Clarke
Department of Geology and Geography
Hunter College-CUNY
695 Park Ave.
New York, NY 10021, USA


Karen A. Mulcahy
Earth and Environmental Science Program
Graduate School and University Center-CUNY
33 West 42nd St.
New York, NY 10036, USA


The Interrupted Modified Collignon or "Clarke's Butterfly" projection is a near-equal area pro- jection of the earth as a sphere onto eight equilateral triangles, arranged as octants. This projection was presented to solve a problem of mapping into an initial set of equilateral triangles that could then be divided recursively into triangular quadtrees based on Dutton's Quaternary Triangular Mesh. This projection was used as a test case for experiments in designing a method for the visu- alization of map projection distortion. We present a new method for portraying the distortion, in which the projection parameters of local shape, area, and direction are shown as several experi- mental combinations of red, green and blue color intensity representations. Some of these combi- nations show distinct promise as visualization methods for map distortion portrayal, and assist greatly in the understanding of the Interrupted Modified Collignon projection's spatial properties. Extension of the method by its incorporation into map projection software is discussed, so that map users will have a simple and effective means to visualize both global maps, and their inherent inaccuracies.

Paper was presented at the GIS/LIS conference, 16th November, 1995 in Nashville, TN.