Marsden square
Encyclopedia
Marsden square mapping or Marsden squares is a system that divides a chart of the world with latitude-longitude gridlines (e.g. plate carrée projection, Mercator
or other) between 80°N
and 70°S
latitudes (or 90°N
and 80°S
: refer chart at Ocean Teacher’s Ocean Geography page) into grid cells of 10° latitude
by 10° longitude
, each with a unique, numeric identifier. 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 one of the 540 10°x10° squares is allocated a number from 1 to 288 and from 300 to 551 (see image to the right), plus the sequence extends to 936 in higher latitudes, and then can also be subdivided into 100 one-degree squares numbered from 00 to 99 in order to improve accuracy.
Marsden squares have mostly been used for identifying the geographic position of meteorological
data, and are described further in various publications of the World Meteorological Organization
(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
but does not seem to be actively promoted by the WMO itself.
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) between 80°N
80th parallel north
The 80th parallel north is a circle of latitude that is 80 degrees north of the Earth's equatorial plane, in the Arctic. It crosses the Atlantic Ocean, Europe, Asia, the Arctic Ocean and North America....
and 70°S
70th parallel south
The 70th parallel south is a circle of latitude that is 70 degrees south of the Earth's equatorial plane in the Antarctic. The parallel passes through the Southern Ocean and Antarctica.Mariners regard the waters in the 70° south as "Godless"....
latitudes (or 90°N
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
and 80°S
80th parallel south
The 80th parallel south is a circle of latitude that is 80 degrees south of the Earth's equatorial plane.It passes through Antarctica and Antarctic ice shelves.Starting at the Prime Meridian and heading eastwards, the parallel 80° south passes through:...
: refer chart at Ocean Teacher’s Ocean Geography page) 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, numeric identifier. 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 one of the 540 10°x10° squares is allocated a number from 1 to 288 and from 300 to 551 (see image to the right), plus the sequence extends to 936 in higher latitudes, and then can also be subdivided into 100 one-degree squares numbered from 00 to 99 in order to improve accuracy.
Marsden squares have mostly been used for identifying the geographic position of meteorological
Meteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
data, and are described further in various publications of the World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...
(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 squares
World Meteorological Organization squares or WMO squares is a system of geocodes that divides a chart of the world with latitude-longitude gridlines into grid cells of 10° latitude by 10° longitude, each with a unique, 4-digit numeric identifier...
but does not seem to be actively promoted by the WMO itself.