## Directory of Map Projections

What is a projection?

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Web maps Mercator

Description

The mathematics for this projection are identical to the standard spherical Mercator. The only distinctions are that the map is limited at 85.051129°N/S to yield a square map, and that geographic coordinates are specified to be given in WGS 84 ellipsoidal datum. This latter stipulation formally causes the projection to be not quite conformal. It is normal to use ellipsoidal coordinates for maps on projections using the sphere as a model because surface features are never surveyed with the assumption of Earth as a sphere and therefore ellipsoidal coordinates what are readily available. This is not normally a problem because the sphere is only used for small- and medium-scale maps, such as of the entire world or of the continents. In those cases, the mapping errors caused by the discrepancy between ellipsoidal and spherical are too small to matter. For large-scale maps, however, the discrepancies become meaningful. It is possible to convert from ellipsoidal to spherical coordinates in order to solve the problem of non-conformality, but Web maps Mercator was developed for street maps, primarily, where perfect conformality is not useful. Meanwhile, correcting for the ellipsoidal discrepancy would be computationally expensive.

Classifications

cylindric
conformal

Aspect

This projection is meaningful only in equatorial aspect.

Graticule

Meridians: Central meridian is straight; others are complex curves.
Parallels: Complex curves.

Scale

High at the top/bottom extremities. However, for large-scale mapping, as a conformal map the scale bar can simply be adjusted to compensate for the inflation.

Distortion

Low near the equator, with inflation increasing away from it.

Similar projections

Spherical equatorial Mercator is mathematically identical.

Origin

Google Maps began using the Web maps Mercator in 2005. It has since appeared in many World Wide Web mapping programs. Google, meanwhile, quit using the projection at small scales on desktop computers in 2016.