SURFACE OF THE EARTH ICOSAHEDRON GLOBE
World Data Service for Geophysics, Boulder
2008 (Store Version Only) has sturdier construction with easy
The Icosahedron as a Map
How do you make a flat sheet of paper into a representation of a spherical object? In particular, how do you make a flat map into a world globe? The ancient Greeks figured out that there were just a few solid objects that could be constructed from certain flat, regular polygons (equilateral triangle, square, or pentagon): tetrahedron (4 triangles), cube (6 squares), octahedron (8 triangles), dodecahedron (12 triangles or 12 pentagons), and icosahedron (20 triangles). With each increase in the number of faces, the regular-sized solid looks more spherical. With 20 faces, the Icosahedron is the best "flat" sphere available.
Each face of the Icosahedron displays a part of the (nearly-spherical) Earth's surface as a flat map in the Gnomonic Projection, tangent at the centroid of the triangle. Folded so that adjacent triangles are joined exactly at their closest edges, the cut-out pattern forms the complete globe with the North and South Poles at opposite vertices. The relief of the continental surface and the sea floor is depicted by shaded colors representing the slope and elevation of the surface of the Earth. Overall size of an assembled globe is approximately 4.5 inches with each side of the individual triangles measuring 2.5 inches. The revised icosahedron includes markings for tabs and corresponding slots, so the globe can be assembled without glue or tape, if desired.
As a class project or a decorative pendant, the Icosahedron Globe will be an amusing and informative exercise. By the way, getting tape on the inside of the last open seam is an exciting challenge to the dexterity of the globe-builder! We definitely advise against Super-Glue (two sided tape is a good choice).
For more information about the new ETOPO1 data set, see http://www.ngdc.noaa.gov/mgg/global/global.html
For more information about bathymetric and topographic data and products, see: http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html We offer posters, slide sets, and digital global relief data on CD-ROM.