Great circles serve as the analog of "straight lines" in spherical geometry. See also spherical trigonometry and geodesic.
Great circles
A great circle on a sphere is a circle that is obtained by intersecting the sphere with a plane containing the center of the sphere.
Great Circle Route:
The shortest distance between two places on the Earth's surface. The route follows a line described by the intersection of the surface with an imaginary plane passing through the Earth's center.
Great circles on the sphere are the analogs of straight lines in the plane. Such curves are often called geodesics. A spherical triangle is a region of the sphere bounded by three arcs of geodesics.
great circle - imaginary circle made on the earth's surface by a plane passing through the center of the earth
small circle - imaginary circle made on the earth's surface by a plane that does not pass through the center of the earth ...
Great Circle
Any line representing the earth’s circumference is known as a great circle, the best known of which is the equator.
Grid ...
a great circle on the celestial sphere on which any point is equidistant from the celestial poles (the plane of the earth's equator, if extended, would coincide with that of the celestial equator)
celestial meridian ...
The great circle formed by the intersection of the plane of the earth's orbit around the sun (or apparent orbit of the sun around the earth) and the celestial sphere.
all great circles - the shortest routes between points on a sphere - are shown as straight lines
4.4 The classification of Map Projections ...
The same great circle (this time covering 360°) and loxodrome in a "Lagrange" conformal map ...
See Also: great circle, latitude
[coordinate systems] The angular distance, usually expressed in degrees, minutes, and seconds, ...
Javascript Great Circle Calculator
Aviation Formulary
Google's Calculator built into their seach engine will do units conversions from meters to feet, miles to kilometers, etc.
meridian -- a great circle on the Earth that passes through the geographic poles.
metadata -- data about the content, quality, condition, and other characteristics of data.
Why the fuss about Great Circles? The answer is that for any two points on the surface of the Earth, the shortest distance between those points is always along a Great Circle. When you look at a map a Great Circle is usually not a straight line.
Great Circle An imaginary circle drawn on the Earth's surface that has its center synchronize to the center of the planet. The equator is a great circle.
The gnomonic is one type of planar projection on which any great circle appears as a straight line. A great circle is the circle created when a plane cuts the Earth through its centre.
Oblique Mercator projections are used to portray regions along great circles. Distances are true along a great circle defined by the tangent line formed by the sphere and the oblique cylinder, elsewhere distance, shape, and areas are distorted.
The Geodesy tool allows users to interactively create great circles and rhumb lines. With Geodesy Calculator, users can specify two coordinates and generate a great circle route, a rhumb line, or a geodesic route.
The measurements will be calculated on great circles, which will be more accurate than measurements made on a projected data frame, unless you have data projected specifically for minimizing distance distortion.
meridian
A meridian is a circular arc (a great circle) 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.
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Lines of Longitude are Great Circles East and West of the Prime Meridian
From Amanda Briney, for About.com
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Displays a geodesic line, tracing the shortest distance between two geographic points along a great circle, in a longitude/latitude data set.
d.graph
Program for generating and displaying simple graphics on the display monitor.
Nautical Mile
A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 meters (about 6,076 feet).
Given two points on a sphere, the shortest path on the surface of the sphere which connects them (the sphere geodesic) is an arc of a circle known as a great circle. The equation of the sphere with points and lying on a diameter is given by
(28) ...
There are several sources of public domain cartographic software that perform cartographic projections as well as other geodetic computations such as compute geodesic distances (Great Circles) and datum transformations.
Commercial ...
angular distance, usually expressed in degrees, minutes, and seconds, of the location of a point on the earth's surface east or west of an arbitrarily defined meridian (usually the Greenwich prime meridian). All lines of longitude are great circles ...
This picture shows P1 and P2 at the centers of crosses in white circles. P1 is on Long Island, New York, and P2 is near Rome, Italy. The thick blue line shows the shortest path between P1 and P2; it is a portion of the great circle containing P1 and ...
meridian Great circle on the surface of the Earth passing through the geographical poles and any given point on the Earth's surface. All points on a given meridian have the same longitude.
 See also: Map, Surface, Projection, Coordinate, Meridian
  
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