World Meteorological Organization squares
Encyclopedia
World Meteorological Organization squares or WMO squares is a system of geocodes
that divides a chart of the world with latitude-longitude gridlines (e.g. plate carrée projection, Mercator
or other) into grid cells of 10° latitude
by 10° longitude
, each with a unique, 4-digit numeric identifier (refer chart at NODC World Ocean Database 2005 page). On the plate carrée projection the grid cells appear square, however if the Mercator projection is used, the grid cells appear 'stretched' vertically nearer the tops and bottoms of the map. On the actual surface of the Globe
, the cells are approximately "square" only adjacent to the equator, and become progressively narrower and tapered (also with curved northern and southern boundaries) as they approach the poles, and cells adjoining the poles are unique in possessing three faces rather than four.
Each 10°x10° square is allocated a number between 1000 and 7817. The numbering system is based first on "global quadrant" numbers where 1=NE, 3=SE, 5=SW, 7=NW which gives the initial digit of any square code (1xxx, 3xxx, 5xxx, 7xxx). The second digit (x0xx through x8xx) indicates the number of tens of degrees latitude (north in global quadrants 1 and 7, south in global quadrants 3 and 5) of the 'minimum' square boundary (nearest to the Equator
), i.e. a cell extending between 10°N and 20°N (or 10°S and 20°S) has this digit = 1, a cell extending between 20°N and 30°N has this digit = 2, etc. The third and fourth digits (xx00 through xx17) similarly indicate the number of tens of degrees of longitude of the 'minimum' square boundary, nearest to the Prime Meridian
. By way of illustration, the square 1000 thus extends from 0°N to 10°N, 0°E to 10°E, and the square 7817 from 80°N to 90°N, 170°W to 180°W, adjacent to the major portion of the International Date Line
. In this manner, reverse-engineering (decoding) the relevant square boundaries from any particular WMO Square identifier is straightforward, in contrast to some other similar systems e.g. Marsden square
s.
WMO squares are also used as the basis for the c-squares
spatial indexing system, which further divides 10°x10° WMO squares into smaller units of 5°x5°, 1°x1°, 0.5°x0.5°, 0.1°x0.1°, and so on.
Geocode
GEOCODE is a standardized all-natural number representation format specification for geospatial coordinate measurements that provide details of the exact location of geospatial point at, below, or above the surface of the earth at a specified moment of time.Geocode is patented under US Patents...
that divides a chart of the world with latitude-longitude gridlines (e.g. plate carrée projection, Mercator
Mercator projection
The Mercator projection is a cylindrical map projection presented by the Belgian geographer and cartographer Gerardus Mercator, in 1569. It became the standard map projection for nautical purposes because of its ability to represent lines of constant course, known as rhumb lines or loxodromes, as...
or other) into grid cells of 10° latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
by 10° longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
, each with a unique, 4-digit numeric identifier (refer chart at NODC World Ocean Database 2005 page). On the plate carrée projection the grid cells appear square, however if the Mercator projection is used, the grid cells appear 'stretched' vertically nearer the tops and bottoms of the map. On the actual surface of the Globe
Globe
A globe is a three-dimensional scale model of Earth or other spheroid celestial body such as a planet, star, or moon...
, the cells are approximately "square" only adjacent to the equator, and become progressively narrower and tapered (also with curved northern and southern boundaries) as they approach the poles, and cells adjoining the poles are unique in possessing three faces rather than four.
Each 10°x10° square is allocated a number between 1000 and 7817. The numbering system is based first on "global quadrant" numbers where 1=NE, 3=SE, 5=SW, 7=NW which gives the initial digit of any square code (1xxx, 3xxx, 5xxx, 7xxx). The second digit (x0xx through x8xx) indicates the number of tens of degrees latitude (north in global quadrants 1 and 7, south in global quadrants 3 and 5) of the 'minimum' square boundary (nearest to the Equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
), i.e. a cell extending between 10°N and 20°N (or 10°S and 20°S) has this digit = 1, a cell extending between 20°N and 30°N has this digit = 2, etc. The third and fourth digits (xx00 through xx17) similarly indicate the number of tens of degrees of longitude of the 'minimum' square boundary, nearest to the Prime Meridian
Prime Meridian
The Prime Meridian is the meridian at which the longitude is defined to be 0°.The Prime Meridian and its opposite the 180th meridian , which the International Date Line generally follows, form a great circle that divides the Earth into the Eastern and Western Hemispheres.An international...
. By way of illustration, the square 1000 thus extends from 0°N to 10°N, 0°E to 10°E, and the square 7817 from 80°N to 90°N, 170°W to 180°W, adjacent to the major portion of the International Date Line
International Date Line
The International Date Line is a generally north-south imaginary line on the surface of the Earth, passing through the middle of the Pacific Ocean, that designates the place where each calendar day begins...
. In this manner, reverse-engineering (decoding) the relevant square boundaries from any particular WMO Square identifier is straightforward, in contrast to some other similar systems e.g. Marsden square
Marsden square
Marsden square mapping or Marsden squares is a system that divides a chart of the world with latitude-longitude gridlines between 80°N and 70°S latitudes into grid cells of 10° latitude by 10° longitude, each with a unique, numeric identifier...
s.
WMO squares are also used as the basis for the c-squares
C-squares
C-squares is a system of geocodes that provides a basis for simple spatial indexing of geographic features or data. It was devised by Tony Rees of CSIRO Marine and Atmospheric Research in 2001-2, and described in the literature in 2003...
spatial indexing system, which further divides 10°x10° WMO squares into smaller units of 5°x5°, 1°x1°, 0.5°x0.5°, 0.1°x0.1°, and so on.