Map Projections
Maps vs. Globe
The only way to accurately represent the Earth is on a globe. Since globes are round like the Earth, they show the correct
shape, location, and relative size of all land and water features. Thus, you can think of a globe as a miniature planet Earth.
Because they're flat, maps can never show a perfect representation of the Earth. Why, then do we use maps? Imagine
having to carry a globe around with you on vacation! Maps are much more convenient than globes for many purposes.
Maps of relatively small areas, such as your state or city, can be drawn with great accuracy, and you get to see the area in
much more. Even maps of larger areas, such as continents or the world, can be drawn with enough accuracy to be useful
and practical for many purposes.
Global Projections
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Azimuthal A type of map in which a flat sheet is placed in contact with a globe, and
points are projected from the globe to the sheet. Directions from the projection's
center to all points are correct. Also called a zenithal projection.
Conic Type of map in which a cone is wrapped around a sphere (the globe), and
the details of the globe are projected onto the conic surface; then, the cone is
unwrapped into a flat surface.
Cylindrical A type of map in which a cylinder is wrapped around a sphere (the
globe), and the details of the globe are projected onto the cylindrical surface;
then, the cylinder is unwrapped into a flat surface, yielding a rectangular-shaped
map. Cylindrical maps have a lot of distortion in the polar regions (that is, the size
of the polar regions is greatly exaggerated on these maps).
Pseudocylindrical A type of projection that, in the normal aspect, has straight
parallel lines for parallels and on which the meridians are usually equally spaced
along parallels (as they are on a cylindrical projection) but on which the meridians
are curved
Cylindrical
If you wrapped a large piece of paper around a globe in the shape of a cylinder, and the continents and bodies
of water once again "jumped" onto the paper, you would have created a cylindrical map projection. Assuming
the globe had been standing "upright," with the North Pole at the top, the paper would have touched the
globe at the equator. The places nearest the equator would therefore be the least distorted on the map. The
closer to the poles, the more distorted the map becomes.
Conic
What if you took a large piece of paper and folded it into a cone (like an ice cream cone or
one of those paper cups at an office water dispenser)? Then you stuck the cone over a
globe so that it covered about half the globe. If the images on the globe "jumped" onto
the paper now, you would have created a conic map projection. The globe and paper
would have touched at one circle around the globe; the map would be the most accurate
around this circle. Look at the example here to see how this works.
Mercator Projection
This is the most commonly-seen map projection, although it is far from the most accurate. Can you guess what type of projection it is
(planar, conic, or cylindrical?). If you guessed cylindrical, you were right. That's why the landforms on this map become increasingly
distorted the farther you get from the equator. Compare the size and shape of Greenland and Antarctica on this map to those landforms
on a globe; the distortion will be obvious. The Mercator map works well for navigational purposes and is a commonly-used "generic"
map that you'll see in magazines, history books, and many other places.
Robinson Projection
The Robinson projection was created to improve upon the shortcomings of previously-existing
projections such as Mercator. It combines the good parts of several other map projections, resulting in
minimal distortion of most of the Earth's land masses. Antarctica is still greatly distorted and the
northernmost land masses are somewhat distorted, but this projection is commonly considered the
best map representation of the size and shape of the Earth's landforms.
Planar (azimuthal)
Imagine placing a piece of cardboard against a globe so that it touches the globe at exactly one point. Now imagine that the
continents and bodies of water on the globe could somehow "jump" from their current location right onto the cardboard. The
cardboard would now contain a map with a planar projection. This type of projection is often used to depict the poles because
the most accurate point of the map is at its center. See the example above.
Goode's Homosoline Projection
Sometimes maps will be interrupted, or divided like this one into segments in
order to reduce distortion and stretching. Goode's interrupted homolosine
projection, as shown here, reduces distortion but breaks the oceans and
Antarctica into pieces. This is an equal-area map because it minimizes distortion in
the size of the landforms. Still, you can notice an obvious distortion in the size of
Antarctica.
Azimuthal
A type of map in which a flat sheet
is placed in contact with a globe,
and points are projected from the
globe to the sheet. Directions from
the projection's center to all points
are correct. Also called a zenithal
projection.
Conic
Type of map in which a cone is wrapped
around a sphere (the globe), and the details of
the globe are projected onto the conic surface;
then, the cone is unwrapped into a flat surface.
Cylindrical
A type of map in which a cylinder is
wrapped around a sphere (the globe), and
the details of the globe are projected
onto the cylindrical surface; then, the
cylinder is unwrapped into a flat surface,
yielding a rectangular-shaped map.
Cylindrical maps have a lot of distortion in
the polar regions (that is, the size of the
polar regions is greatly exaggerated on
these maps).
Pseudocylindrical
A type of projection that, in the normal
aspect, has straight parallel lines for parallels
and on which the meridians are usually
equally spaced along parallels (as they are
on a cylindrical projection) but on which the
meridians are curved.
Map of the World, 1595
Map of the World, 1664
Map of the World, 1664