Marsden square

Marsden square mapping or Marsden squares is a system that divides a world map 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) into grid cells of 10° latitude by 10° longitude, each with a geocode, a unique numeric identifier.

1754, d. 1836), when first secretary of the British Admiralty, for collecting and combining geographically based information about the oceans.

[1] 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, 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.

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.