Glossary

aspect

Conceptual placement of a projection system in relation to the Earth's axis (direct, normal, polar, equatorial, oblique, and so on)

azimuthal projection

Projection on which the azimuth or direction from a given central point to any other point is shown correctly. Also called a zenithal projection. When a pole is the central point, all meridians are spaced at their true angles against and are straight radii of concentric circles that represent the parallels

central meridian

Meridian passing through the center of a projection, often a straight line about which the projection is symmetrical

conformal projection

Projection on which all angles at each point are preserved. Also called an orthomorphic projection

conic projection

Projection resulting from the conceptual projection of the Earth onto a tangent or secant cone, which is then cut lengthwise and laid flat. When the axis of the cone coincides with the polar axis of the Earth, all meridians are straight equidistant radii of concentric circular arcs representing the parallels, but the meridians are spaced at less than their true angles. Mathematically, the projection is often only partially geometric

cylindrical projection

Projection resulting from the conceptual projection of the Earth onto a tangent or secant cylinder, which is then cut lengthwise and laid flat. When the axis of the cylinder coincides with the axis of the Earth, the meridians are straight, parallel, and equidistant, while the parallels of latitude are straight, parallel, and perpendicular to the meridians. Mathematically, the projection is often only partially geometric

equal-area projection

Projection on which the areas of all regions are shown in the same proportion to their true areas. Also called an equivalent or authalic projection. Shapes may be greatly distorted

equatorial aspect

Aspect of an azimuthal projection on which the center of projection or origin is some point along the Equator. For cylindrical and pseudocylindrical projections, this aspect is usually called conventional, direct, normal, or regular rather than equatorial

equidistant projection

Projection that maintains constant scale along all great circles from one or two points. When the projection is centered on a pole, the parallels are spaced in proportion to their true distances along each meridian

graticule

Any circle on the surface of a sphere, especially when the sphere represents the Earth, formed by the intersection of the surface with a plane passing through the center of the sphere. It is the shortest path between any two points along the circle and therefore important for navigation. All meridians and the Equator are great circles on the Earth taken as a sphere

latitude (geographic)

Angle made by a perpendicular to a given point on the surface of a sphere or ellipsoid representing the Earth and the plane of the Equator ('+' if the point is north of the Equator, '-' if it is south). One of the two common geographic coordinates of a point on the Earth

latitude of origin

The intersection of the latitude of projection origin and the central meridian defines the origin (0,0) of the projected coordinate grid

longitude

Angle made by the plane of a meridian passing through a given point on the Earth's surface and the plane of the (prime) meridian passing through Greenwich, England, east or west to 180 degrees ('+' if the point is east, '-' if it is west). One of the two common geographic coordinates of a point on the Earth.

normal aspect

See Direct aspect

oblique aspect

Aspect of a projection on which the center of projection or origin is located at a point which is neither at a pole nor along the Equator

parallel

Small circle on the surface of the Earth formed by the intersection of the surface of the reference sphere or ellipsoid with a plane parallel to the plane of the Equator. This line is identified by its latitude. The Equator (a great circle) is usually also treated as a parallel

perspective projection

Projection produced by projecting straight lines radiating from a selected point (or from infinity) through points on the surface of a sphere or ellipsoid and then onto a tangent or secant plane. Other perspective maps are projected onto a tangent or secant cylinder or cone by using straight lines passing through a single axis of the sphere or ellipsod. Also called geometric projection

planar projection

Projection resulting from the conceptual projection of the Earth onto a tangent or secant plane. Usually, a planar projection is the same as an azimuthal projection. Mathematically, the projection is often only partially geometric

polar aspect

Aspect of a projection, especially an azimuthal one, on which the Earth is viewed from the polar axis. For cylindrical or pseudocylindrical projections, this aspect is called transverse

pseudocylindrical projection

Projection that, in the normal aspect, has straight parallel lines for parallels and on which the meridians are (usually) spaced along parallels, as they are on a cylindrical projection, but on which the meridians are curved

standard parallel

In the normal aspect of a projection, a parallel of latitude along which the scale is as stated for that map. There are one or two standard parallels on most cylindrical and conic map projections and one on many polar stereographic projections