Mercator Projection



The famous conformal cylindrical projection. It is excellent for the limited purpose of marine navigation. A modification of the Mercator, the Pseudo-Mercator projection, has become the universal choice of web servers such as Bing and Google.  The Pseudo-Mercator projection is used by Manifold as the default projection.   See the Transverse Mercator topic for the transverse aspect of this projection.




True along the Equator and along two chosen standard parallels equidistant from the Equator.


Increases with distance from the Equator to infinity at the poles.


Scale is constant along any given parallel; same scale at parallel of opposite sign (north +, south -) and is the same in all directions near any given point.




Infinitesimally small circles of equal size on the globe appear as circles on the map (indicating conformality) but increase in size away from the Equator (indicating area distortion). Great distortion of area in polar regions. Conformality (and therefore local angle preservation) fails at the poles. Low distortion near the Equator.




Designed and recommended for navigational usage because of straight rhumb lines; standard for marine charts. Recommended and used for conformal mapping of regions predominantly bordering the Equator. The Mercator projection attained great fame because of its utility for marine navigation.


One unfortunate result of this fame is that it subsequently was frequently and inappropriately used as a thematic world map in atlases and for wall charts. It presents a highly misleading view of the world because of the excessive distortion of area away from the poles.  A case in point is the classic schoolroom map of the Earth in Mercator projection that has convinced generations of school children that Greenland is as large as North America.


See the Gall projection topic for additional discussion of the Mercator projection, why it is especially useful in the Third World and the evil political attack on its usage.




Presented by Gerardus Mercator (1512-1594) of Flanders in 1569 on a large world map "for use in navigation".




Gerardus Mercator


A 1532 masters graduate of the University of Louvain, Mercator was originally known as Gerard de Cremere. He worked mainly in Louvain and Duisburg, where he produced most of his famous maps and was appointed Court Cosmographer to Duke Wilhelm of Cleve.


Mercator had moved to Duisburg in 1552 after the University of Louvain interceded to have him freed from prison where he had languished for seven months after being charged with heresy in 1544 after travels related to his cartographic work. He was the first to use the term atlas to refer to a collection of maps.


Mercator also invented a process for mass production of globes. In earlier times globes were produced using a labor-intensive process of engraving directly upon solid spheres. Mercator created papier-mâché, hollow globes to which he glued mass produced, hand-colored, paper engravings shaped in the now-familiar 12 gores (shapes narrowing towards the poles) plus two circular polar end caps. He produced several hundred terrestrial and celestial globes mounted in wooden stands, of which 22 matched pairs are still extent.


Over 450 years after his imprisonment, Mercator continues to be assaulted by the technologically inept but politically well-connected. See the discussion of the vicious propaganda movement using the Gall projection in the Gall topic for the latest political assault on Mercator.


Limiting Forms


A Transverse Mercator projection is achieved when the Mercator projection's cylinder is rotated about the Earth so that instead of the Equator being the central ring of the cylinder a Meridian (that is, a longitude line) becomes the central ring.




Specifying a non-Equatorial latitude origin causes an oblique projection.


Notes on Default Use of Pseudo-Mercator Projection


Manifold uses Pseudo-Mercator projection as a default projection when nothing is known about the geographic context of a component.


Components imported into Manifold from geographically aware formats will automatically use whatever geographic context or projection is defined in the source file(s). Components such as images and CAD drawings imported from non-geographic formats will be imported as if they were in a meter-based Pseudo-Mercator projection. Such components may acquire a geographic context at some point by georegistration or by otherwise assigning a projected coordinate system but initially they are created in meter-based or pixel-based coordinate systems.


It makes sense to consider such components as being in Pseudo-Mercator projection. Considering the small size of CAD drawings or images relative to the size of an entire Earth hemisphere, there is an essentially perfect correlation between the flat, Euclidean coordinates of the drawing or image space and the effectively flat, Euclidean coordinates of the very central portion of a Pseudo-Mercator projection.


This convention of considering all abstract coordinate CAD drawings and pixel coordinate images to be loaded within a Pseudo-Mercator projection provides three main benefits: