The Cahill–Keyes projection is a polyhedral compromise

map projection In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longit ...

first proposed by Gene Keyes in 1975. The projection is a refinement of an earlier 1909 projection by Bernard Cahill. The projection was designed to achieve a number of desirable characteristics, namely symmetry of component maps (octants), scalability allowing the map to continue to work well even at high resolution, uniformity of

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s, metric-based joining edges, minimized distortion compared to a globe, and an easily understood orientation to enhance general usability and teachability.

Construction

The Cahill–Keyes projection was designed with four fundamental considerations in mind: visual fidelity to a globe, proportional

s, 10,000 km lengths for each of its octants' three main joined edges, and an M-shape Master-Map profile. The resulting map comprises 8 octants. Each octant is an

equilateral triangle In geometry, an equilateral triangle is a triangle in which all three sides have the same length. In the familiar Euclidean geometry, an equilateral triangle is also equiangular; that is, all three internal angles are also congruent to each oth ...

with three segments per side. One side runs along the equator, and the other two run along meridians. The total length of each side is 10,043 km. The inner meridians converge towards the

pole Pole may refer to: Astronomy *Celestial pole, the projection of the planet Earth's axis of rotation onto the celestial sphere; also applies to the axis of rotation of other planets *Pole star, a visible star that is approximately aligned with the ...

. Each 1° and 5° "tile" is proportional to each other. The specific process for constructing the

graticule Graticule may refer to: * An oscilloscope graticule scale * The reticle pattern in an optical instrument * Graticule (cartography), a grid of lines on a map See also * Grid (disambiguation) Grid, The Grid, or GRID may refer to: Common us ...

divides each half-octant into twelve zones, each of which has different formulae for coordinate calculations.Gene Keyes
"Cahill-Keyes Octant Graticule: Principles and Specifications"
''Gene Keyes Website'', 2010-08-20

References

External links

Gene Keyes's Cahill-Keyes and Cahill resource index

D3.js Implementation of Cahill–Keyes Projection

{{DEFAULTSORT:Cahill-Keyes projection Map projections