Bonne projection

A Bonne projection is a pseudoconical equal-area map projection, sometimes called a dépôt de la guerre or a Sylvanus projection. Although named after Rigobert Bonne (1727–1795), the projection was in use prior to his birth, in 1511 by Sylvano, Honter in 1561, De l'Isle before 1700 and Coronelli in 1696^[1].

The projection is:

x=\rho \sin E\,

y=\cot \varphi _{1}-\rho \cos E\,

where

\rho =\cot \varphi _{1}+\varphi _{1}-\varphi \,

E={\frac {\lambda \cos \varphi }{\rho }}

and φ is the latitude, λ is the longitude from the central meridian, and φ₁ is the standard parallel of the projection^[2].

Parallels of latitude are concentric circular arcs, and the scale is true along these arcs. On the central meridian and the standard latitude shapes are not distorted.

Special cases of the Bonne projection include the sinusoidal projection, when φ₁ is zero, and the Werner projection, when φ₁ is π/2. The Bonne projection can be seen as an intermediate projection in the unwinding of a Werner projection into a Sinusoidal projection; an alternative intermediate would be a Bottomley projection^[3]

References

^ Flattening the Earth: Two Thousand Years of Map Projections, John P. Snyder, 1993, pp.60-62, ISBN 0-226-76747-7
^ Map Projections - A Working Manual, USGS Professional Paper 1395, John P. Snyder, 1987, pp.138-140
^ Between the Sinusoidal projection and the Werner: an alternative to the Bonne, Henry Bottomley 2002

External links

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[1] Flattening the Earth: Two Thousand Years of Map Projections, John P. Snyder, 1993, pp.60-62, ISBN 0-226-76747-7

[2] Map Projections - A Working Manual, USGS Professional Paper 1395, John P. Snyder, 1987, pp.138-140

[3] Between the Sinusoidal projection and the Werner: an alternative to the Bonne, Henry Bottomley 2002

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