| The term polyconic is generically applied to any projection with circular arcs for parallels of latitude, whether or not they are concentric |
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(Simple) Polyconic projection
- The projection is true to scale along the central meridian and along each parallel. It is neither conformal nor equal-area, and it is only free of distortion along the central meridian. Therefore, it should only be used for regions of predominant north-south extent
- The polyconic was applied as a specific projection in 1853 by the US Coast Survey. It was commonly, but not exclusively, used for coastal charts of the United States. The emphasis on usage by US government agencies led to its use in several 19th century commercial atlases as well, for some maps of the United States, Canada, North America, Asia and Oceania.
The polyconic projection of Hassler is simultaneously universal for a given figure of the earth (sphere or ellipsoid), simply drawn, even for the ellipsoid, and employs useful scale characteristics.
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Rectangular polyconic projection
- Neither conformal nor equal-area
- The first reference to this projection was made in 1853. This projection was derived and used at that time by the U.S. Coastal Survey for portions of the United States exceeding about a square degree. It has since been used for topographic maps of the British War Office and thus has been called the War Office projection as well.
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Bonne's pseudoconic projection
- Equal-area
- The Bonne was the preferred projection for atlas maps of large countries and continents, giving the regions a uniform area scale and an appealing combination of curved meridians and curved parallels befitting a representation of the globe. More than half the maps of the world's most populated continents were prepared on the Bonne projections.
- The Bonne projection played a significant role in 19th century larger-scale topographic mapping using ellipsoidal formulas. This began with its adoption in France after efforts by Bonne in 1802, when his projection was accepted by a special commission of the Depot de la Guerre (war office). It later received the name projection depot de la guerre in other European countries. These regions included Austria-Hungary (1:750,000 scale maps), Belgium (1:20,000 and reductions), Denmark (1:20,000), Italy (1:500,000), Netherlands (1:25,000), Russia (1:126,000), Spain (1:200,000), Switzerland (1:25,000 and 1:50,000), Scotland and Ireland (1:63,360 and smaller), as well as France (1:80,000 and 1:200,000) (Hinks 1912).
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Werner (Stabius) pseudoconic projection
- Equal-area
- Heart-shaped (also referred to as cordiform and cardioid)
- In 1514, Stabius invented a series of three attractive heart-shaped projections which were further publicized by Werner.
- After sporadic usage, the cordiform projection all but disappeared by the 18th century in favour of the Bonne projection. This more general adaptation of Werner's projection provides less angular distortion for a map of a continent.
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Van der Grinten projection
- Compromise, but huge distortion on high latitudes
- The whole Earth is represented on a circle
- Both paralles and meridians are circular arcs
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