Graticule

From Geohashing
Revision as of 12:07, 11 June 2009 by 125.60.28.21 (talk) (Shape)

A graticule is a network of geographic lines. We use it to refer to the rectangular[1] zones between the latitude and longitude lines, each 1°×1° in size.

A graticule may be divided into 100 centicules in a 10×10 grid.

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Numbering

Graticules are numbered with a pair of numbers based on the corner closest to N0°, E0°, so that the graticule a location belongs to can be determined by truncating the degree fraction.

Note that in this numbering 0 is not the same as -0: graticules immediately west of the Greenwich meridian have the east/west part -0°, and graticules immediately south of the equator have the north/south part -0°. For example, graticule (52, 0) is Cambridge, United Kingdom, whereas graticule (52, -0) is the next graticule westwards, Northampton, United Kingdom.

There are 360 x 180 = 64,800 graticules on the globe. So far only a fraction of these have been named and an even smaller fraction actually geohashed. A majority lie in open water.

Footnotes

  1. ^ It isn't entirely true that the graticules mark out a rectangular chunk of ground. The side of the graticule closer to the equator will be larger than the one closer to the pole, leading to something more akin to a trapezium. In the limit, at the north and south poles, the graticules become triangular. Add to this the additional complexity of the curvature of the earth and any discussion of the shape of a graticule is either hideously technical or an oversimplification. On the Mercator projection used by Google Maps however, the earth is distorted so that the shape is, in fact, rectangular.