Map Projections, Geography Glossary - EnchantedLearning.com

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Types of Maps:
Projections
Geography Glossary
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A map is a representation of a place. There are many different types of maps that have different uses.

Projections: Maps are called projections because map-makers have to project a 3-D surface onto a 2-D map. A projection is a representation of one thing onto another, such as a curved 3-Dimensional surface (like the Earth) onto a flat 2-Dimensional map. There are 3 major types of projections: cylindrical, conic, and planar.

Since a map is 2-dimensional representation of a 3-dimensional world, compromises must be made in accuracy (some information must be lost when one dimension is ignored). Different maps differ in the relative accuracy of the depiction of the area, the shapes of objects, actual distances, and compass direction. Maps that focus on maintaining one feature (like preserving distance) must distort other features (like area, shape and compass directions).

Maps that accurately reflect area are often called equal-area maps (an example is the Albers equal-area conic map). Maps that maintain the shape of objects are called conformal. Maps that correctly show the distance between points are often called equi-distant maps (note that the shortest distance between two points on a map is generally not a straight line. but a curve). Navigational maps need accurate compass directions maintained on the map (like the Mercator map).

Related Terms:

central meridian
A central meridian is a meridian that passes through the center of a projection. The central meridian is often a straight line that is an axis of symmetry of the projection.

conic projection
A conic projection is a type of map in which a cone 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.

cylindrical projection
A cylindrical projection is 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).

equator
The equator is an imaginary circle around the earth, halfway between the north and south poles.

geographical coordinate system
A geographical coordinate system is a system that uses latitude and longitude to describe points on the spherical surface of the globe.

latitude
Latitude is the angular distance north or south from the equator to a particular location. The equator has a latitude of zero degrees. The North Pole has a latitude of 90 degrees North; the South Pole has a latitude of 90 degrees South.

longitude
Longitude is the angular distance east or west from the north-south line that passes through Greenwich, England, to a particular location. Greenwich, England has a longitude of zero degrees. The farther east or west of Greenwich you are, the greater your longitude. Midway Islands (in the Pacific Ocean) have a longitude of 180 degrees (they are on the opposite side of the globe from Greenwich).

Mercator projection
A Mercator projection is a type of rectangular map in which the true compass direction are kept intact (lines of latitude and longitude intersect at right angles), but areas are distorted (for example, polar areas look much larger than they really are). Mercator projections are useful for nautical navigation. Geradus Mercator devised this cylindrical projection for use in navigation in 1569.

meridian
A meridian a circular arc of longitude that meets at the north and south poles and connects all places of the same longitude. The prime meridian (0 degrees longitude) passes through Greenwich, England.

Mollweide projection
A Mollweide projection is a type of sinusoidal projection map in which the entire surface of the Earth is shown within an ellipse. Lines of latitude are parallel to the equator, but lines of longitude are curved in such a way that area distortion is minimal. The distortion is greatest at the edges of the ellipse. This type of projection was created by Carl B. Mollweide in 1805.

Orthographic projection
An Orthographic projection is a type of map in which is essentially a drawing of (one side of) a globe. There is a lot of distortion of area in this type of map, but one gets the idea that the globe is being represented.

Orthophanic projection
The Orthophanic (meaning 'right appearing') projection, also called the Robinson projection, is a widely-used type of map in which the Earth is shown in a flattened ellipse. In this pseudocylindrical. projection, lines of latitude are parallel to the equator, but lines of longitude are elliptical arcs. In a Robinson projection, area is represented accurately, but the distances and compass directions are distorted (for example, compass lines are curved). This type of projection was first made in 1963 by Arthur H. Robinson.

parallel
A parallel (of latitude) is a line on a map that represents an imaginary east-west circle drawn on the Earth in a plane parallel to the plane that contains the equator.

planar projection
A planar projection is a type of map in which the details of the globe are projected onto a plane (a flat surface) yielding a rectangular-shaped map. Cylindrical maps have a lot of distortion towards the edges.

Robinson projection
The Robinson projection is a widely-used type of map in which the Earth is shown within an ellipse with a flat top and bottom. In this pseudocylindrical. projection, lines of latitude are parallel to the equator, but lines of longitude are elliptical arcs. In a Robinson projection, area is represented accurately, but the distances and compass directions are distorted (for example, compass lines are curved). This type of projection was first made in 1963 by Arthur H. Robinson; it is also called the Orthophanic projection (meaning 'right appearing').

sinusoidal projection
A sinusoidal projection is a type of map projection in which lines of latitude are parallel to the equator, and lines of longitude are curved around the prime meridian.

Winkel Tripel projection
A Winkel Tripel projection is a type of pseudocylindrical projection map in which both the lines of latitude and longitude are curved. The Winkel Tripel projection was adopted by the National Geographic Society in the late 1990s (replacing the Robinson projection).