Summaries of Map Projections
Mercator
This projection comes from the idea of wrapping a piece of paper around a globe to make a cylinder. Such a map shows
shapes fairly accurately but not size or distance. By stretching the globe into a rectangle, this projection exaggerates lands
away from the equator so that areas near the Poles are quite distorted. Thus, Greenland and Alaska appear much larger than
they do on a globe. With a Mercator projection, you’d never know that Greenland is eight times smaller than South America.
However, because true directions are shown, a Mercator map is very useful for sea travel and allows navigators to plot a
straight course between any two points on Earth.
Robinson
On many projections, Earth’s features seem too small, too big, or just deformed. The Robinson projection was designed to
show landforms much the way they really look. It was used by National Geographic for several years because it was
considered to be a visually appealing way to show the entire world. This projection has minor, but not major, distortions.
Robinson maps show lines of latitude as parallel straight lines and lines of longitude as nonparallel lines that become
increasingly curved as you move farther away from the map's central meridian. The poles are shown as straight lines and the
east and west edges of the map are curved lines 180° from the map's central meridian. The lines of latitude and longitude do
not intersect in right angles on this map making it hard to navigate, however it does show land masses in much more
proportionate sizes. The sizes and shapes near the eastern and western edges of the map are accurate, and the outlines of the
continents appear much as they do on a globe. However, the shapes of areas near the poles appear somewhat flat.
Gall-Peters
This projection uses a rectangular coordinate system that shows parallel lines of latitude and longitude. Therefore, it has
standard parallels of 45 degrees creating inaccurate distances. The Peters Map of the World shows the earth's geographic
relationships better because the sizes of landmasses are accurate. In particular, South America, Africa, and Southeast Asia are
shown in their correct size relationship to Europe and North America. Their shapes, however, are greatly distorted.
Planar (Azimuthal)
Project the Earth onto a plane that touches—or, technically, is tangent to—the globe at a single point, and you get a planar
projection. This projection is also known as an Azimuthal or a zenithal projection which means that it is a map projection in
which the direction from a given central point to any other point is shown correctly. Because this projection is most accurate
at its center with stretching visible at the far edges, it is often used for maps focusing on one of the Poles. However, focusing
on one of the Poles means these maps may only depict half the Earth at a time. This type of projection is often referred to as
planar, azimuthal, or flat-plane.
Conic
This projection is achieved by placing a cone on top of either pole. The map will be least distorted along the parallel where
the cone touches the sphere. This means distance and directions are fairly accurate along the reference parallels. Conic
projections are not widely used in mapping because of their relatively small zone of reasonable accuracy. The scale of the
map rapidly becomes distorted as distance from the correctly represented parallel increases. Because of this problem, conic
projections are best suited for maps of mid-latitude regions, especially those elongated in an east- west direction. The United
States meets these qualifications and therefore is frequently mapped on conic projections.
Goode’s Interrupted Equal-Area
This projection is an equal-area composite map projection which is interrupted to reduce distortion in the major land masses.
On an equal-area projection, the size of any area on the map is in true proportion to its size on the earth. All the major
continents, with the exception of Antarctica, are intact. The projection is often presented with repeated sections so that
Greenland and the eastern tip of Siberia are not interrupted. The Goode’s Interrupted Equal-Area projection was designed to
reduce the shape and sizes of land masses however it interrupts the oceans and land mass of Antarctica (which distorts
perception of direction and distance). Equal-area maps are good for showing the density of an attribute with dots, the spatial
extent of a categorical attribute (for example, land use maps), or quantitative attributes by area (for example, Gross Domestic
Product by country).
Summaries of Map Projections
http://www.geography.hunter.cuny.edu/mp/mpbasics.html
http://en.wikipedia.org/wiki/Map_projection
http://www.autopano.net/wiki-en/action/view/Understanding_Projecting_Modes#Planar_or_rectilinear_projection