The available projections with OMC

OMC Projections

GMT offers more than 20 different projections for mapping or data plotting. Six of them are implemented at the OMC:

1. Mercator Projection
2. Equidistant Cylindrical Projection
3. Polar Stereographic Projection
4. Lambert Azimuthal Equal-Area Projection
5. Azimuthal Equidistant Projection
6. Orthograpic Projection

The first two projections will always present a rectangular map of the area specified. With the exception that areas north of 85°N or south of 85°S are not displayed if you choose the Mercator projection.

Areas displayed under projection number three (Polar Stereographic Projection) will be drawn as wedge-shaped maps for smaller east-west coverages. You will receive a full-circle-figure for a east-west extension of 360°.

A map of the fourth projection (Lambert Azimuthal Equal-Area Projection) will be shown to you as a rectangular figure if you define small or middle sized areas. For larger maps you will get a view on an entire hemisphere with the area specified plotted in the map center.

Projection number five (Azimuthal Equidistant Projection) returns a circular plot of the entire world with the area of interest as the center, distances measured from there are true. The location 180° away from the center is the circumference of this figure.

The Orthographic Projection will always return a hemispherical view to you. The area of your interest again lies in the center of the map.

From the GMT (v.3.0) manual, by P.Wessel and W.H.F.Smith:

Mercator Projection

Probably the most famous of the various map projections, the Mercator projection takes its name from Mercator who presented it in 1569. It is a cylindrical, conformal projection with no distortion along the equator. A major navigational feature of the projectioen is that a line of constant azimuth is straight. Such line is called a rhumb line or loxodrome. Thus, to sail from one point to another one only had to connect the points with a straight line, and keep this constant course for the entire voyage. The Mercator projection has been used extensively for world maps im which the distortion towards the polar regions grows rather large, thus incorrectly giving the impression that, for example, Greenland is larger than South America. Also, the former Soviet Union looks much bigger than Africa or South America. [...]

Equidistant Cylindrical Projection

This simple cylindrical projection is really a linaer scaling of longitudes and latitudes [...] It is also known as the Plate Carée projection. All meridians and parallels are straight lines.

Polar Stereographic Projection

This [the Stereographic Equal-Angle Projection with the Polar Stereographic Projection as a special case, M.W.]is a conformal, azimuthal projection that dates back to the Greeks. It's main use is for mapping the polar regions. In the polar aspect [!] all meridians are straight lines and parallels are arcs of circles.

Lambert Azimuthal Equal-Area Projection

This projection was developed by Lambert in 1772 and is typically used for mapping large regions like continents and hemispheres. It is an azimuthal, equal area projection, but is not perspective. Distortion is zero at the center of the projection, and increases radially away from this point.

Azimuthal Equidistant Projection

The most noticeable feature of this azimuthal projection is the fact that distances measured from the center (of the map) are true. Therefore, a circle about the projection center defines the locus of points that are equally far away from the plot origin. Furthermore, directions from the center are also true. The projection, in the polar aspect, is at least several centuries old. It is a useful projection for a global view of locations at various or identical distance from a given point (the map center).

Orthographic Projection

The orthographic azimuthal projection is a perspective projection from infinite distance. It is therefore often used to give the appearance of a globe viewed from space. As with Lambert's equal areal and the stereographic, only one hemisphere can be viewed at any time. The projection is neither equal area nor conformal, and much distortion is introduced near the edge of a hemisphere. The directions from the center of projection are true. The projection was known to the Egyptians and Greeks more than 2,000 years ago.