Marsden square mapping or Marsden squares is a system that divides a

world map A world map is a map of most or all of the surface of Earth. World maps, because of their scale, must deal with the problem of projection. Maps rendered in two dimensions by necessity distort the display of the three-dimensional surface of ...

with

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...

longitude Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek let ...

gridlines (e.g. plate carrée projection,

Mercator __NOTOC__ Mercator (Latin for "merchant") may refer to: People * Marius Mercator (c. 390–451), a Catholic ecclesiastical writer * Arnold Mercator, a 16th-century cartographer * Gerardus Mercator, a 16th-century cartographer ** Mercator 1569 ...

or other) between 80°N and 70°S latitudes (or 90°N and 80°S: refer chart at Ocean Teacher’
Ocean Geography
page) into grid cells of 10° latitude by 10° longitude, each with a

geocode A geocode is a code that represents a geographic entity ( location or object). It is a unique identifier of the entity, to distinguish it from others in a finite set of geographic entities. In general the ''geocode'' is a human-readable an ...

, a unique numeric identifier. The method was devised by William Marsden (b. 1754, d. 1836), when first secretary of the

British Admiralty The Admiralty was a department of the Government of the United Kingdom responsible for the command of the Royal Navy until 1964, historically under its titular head, the Lord High Admiral – one of the Great Officers of State. For much of i ...

, for collecting and combining geographically-based information about the oceans.

Structure and design

On the plate carrée projection the grid cells appear square, although 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 A globe is a spherical model of Earth, of some other celestial body, or of the celestial sphere. Globes serve purposes similar to maps, but unlike maps, they do not distort the surface that they portray except to scale it down. A model glo ...

, 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 of the 540 10°x10° squares is allocated a unique number from 1 to 288 and from 300 to 551 (see image to the right), plus the sequence extends to 936 in higher latitudes; individual squares can also be subdivided into 100 one-degree squares numbered from 00 to 99 in order to improve precision.

Use

Marsden squares have mostly been used for identifying the geographic position of

meteorological Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...

data, and are described further in various publications of the

World Meteorological Organization The World Meteorological Organization (WMO) is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. The WMO originated from the Inter ...

(WMO). The 10°x10° square identifiers typically use a minimal number of characters (between 1 and 3 digits) which was/is an operational advantage for low bandwidth transmission systems. However the rules for allocating numbers to squares do not follow a consistent pattern, so that reverse-engineering (decoding) the relevant square boundaries from any particular Marsden Square identifier is not particularly straightforward (a look-up table is probably the simplest in practice). Slightly confusingly, an alternative (and more consistent), four-digit notation for global 10°x10° squares is actually known as

World Meteorological Organization squares World Meteorological Organization (WMO) squares is a system of geocodes that divides a world map with latitude-longitude gridlines into grid cells of 10° latitude by 10° longitude, each with a unique, 4-digit numeric identifier (refer chart at ...

but does not seem to be actively promoted by the WMO itself.

Notes

{{Geocoding-systems Geocodes