About the Sinusoidal Projection
The Sinusoidal projection has its origins in the Renaissance although there are a number of possible inventors. Jehan Cossin of Dieppe appears to be the first to use the projection in a world map dated 1570. Many contemporary maps appear to be sinusoidal but actually have meridians that are circular arcs and not sinusoids. However a true sinusoidal projection was used by Hondius for maps of South America and Africa in some of his editions of Mercator's atlases from 1606 to 1609. This appears to be the origin of the pseudonym "Mercator equal-area projection" - even though Mercator never used this projection! Nicolas Sanson d'Abbeville of France, and John Flamsteed of England both used it during the 17th century, which has also led to the common pseudonym of "Sanson-Flamsteed". John Flamsteed, the first Astronomer Royal, only used the sinusoidal projection for celestial maps.
The Sinusoidal projection is a pseudo-cylindrical projection. Ie. a mathematical projection with straight line parallels (like a cylindrical projection) but with curved meridians (unlike a cylindrical projection). With the exception of the central meridian, all of the meridians in the Sinusoidal projection are sine curves. This results in a projection which shows less shape distortion than the Behrmann Cylindrical Equal Area projection.
Author's Note: Of the projections presented here at Equal-Area-Maps.com, the Sinusoidal projection is one of the most practical for online mapping with support from ESRI, Proj4, and Proj4JS. However, it shows greater shape distortion than the Mollweide projection, and is generally less aesthetically pleasing.