The Bonne projection is a pseudoconical equal-area map projection, sometimes called a dépôt de la guerre, modified Flamsteed, or a Sylvanus projection. Although named after Rigobert Bonne (1727–1795), the projection was in use prior to his birth, by Sylvanus in 1511, Honter in 1561, Coronelli in 1696 and De l'Isle before 1700. Both Sylvanus and Honter's usages were approximate, however, and it is not clear they intended to be the same projection.
The Bonne projection maintains accurate shapes of areas along the central meridian and the standard parallel, but progressively distorts away from those regions. Thus, it best maps "t"-shaped regions. It has been used extensively for maps of Europe and Asia.
The projection is defined as:
where
and is the latitude, is the longitude, is the longitude of the central meridian, and is the standard parallel of the projection.Map Projections - A Working Manual , USGS Professional Paper 1395, John P. Snyder, 1987, pp. 138–140
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.
The inverse projection is given by:
where
taking the sign of .
Special cases of the Bonne projection include the sinusoidal projection, when is zero (i.e. the Equator), and the Werner projection, when is 90° (i.e. the North or South Pole). 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.Between the Sinusoidal projection and the Werner: an alternative to the Bonne, Henry Bottomley 2002
See also
List of map projections
References
External links
Table of examples and properties of all common projections, from radicalcartography.net An interactive Java Applet to study the metric deformations of the Bonne Projection Bonne Projection (wolfram.com)