Cassini-Soldner Projection



Also known simply as the Cassini projection.  A cylindrical projection that is neither conformal nor equal-area.




True along central meridian and along lines perpendicular to central meridian. Scale is constant but not true along lines parallel to central meridian on spherical form, nearly so for ellipsoid.




There is no distortion along the central meridian if it is maintained at true scale (the usual case).




Used for topographic mapping formerly in England and currently in a few other countries. Although the Cassini projection has been largely replaced by the Transverse Mercator, it is still in limited use outside the United States and was one of the major topographic mapping projections until the early 20th Century.




Devised by Cesar Francois Cassini de Thury (1714 - 1784) in 1745 for the survey of France.  C.F. Cassini was the grandson of Jean Dominique Cassini, the famous Italian-born astronomer who changed his name from Giovanni Domenico after being hired in 1669 for astronomical research in Paris. J.D. Cassini began the survey of France and C.F. Cassini was the third of four generations involved in this project, the first detailed survey of a nation.




Jean Dominique Cassini (1625 – 1712)


The great astronomer who began the Cassini survey of France, which continued over four generations and with his grandson Cesar transformed into the creation of the Cassini Map of France.  Discovered the Cassini division of the rings of Saturn and four moons of Saturn.  The founder and first director of the Paris Observatory and astronomer to Louis XIV.




Jacques Cassini (1677 – 1756)


Born at the Paris Observatory and succeeded his father as the head of the Paris Observatory. Continued the work of his father surveying France.




Cesar Francois Cassini de Thury (1714 – 1784)


Third in the family to direct the Paris Observatory, inventor of the Cassini projection and the initiator of the Cassini Map.




Jean-Dominique, comte de Cassini (1748 – 1845)


Born at the Paris Observatory and fourth in his family to direct the Paris Observatory. Against all odds brought the Cassini Map project to completion in 1793 despite the revolution but was thrown into prison in 1794.  He survived seven months in prison until his release and then continued his work from the family estate in Thury, writing a history of the Paris Observatory and publishing the autobiography of his illustrious great-grandfather.