Recognizing the need for areal breakdown, the CWP has suggested that a graticule-based system could be used throughout the globe and has recommended that the quadrangles (also called rectangles or squares) be coded and identified according to the following standard rules:

a) the identification of the latitude should be given before that of the longitude;

b) each quadrangle (rectangle) should be identified by its graticule-based boundaries as defined by the latitude and the longitude meeting in its corner nearest to the point where the Equator is crossed by the Greenwich Meridian;

c) the foregoing data on latitude and longitude should be preceded by (i) the first digit identifying the size of the quadrangle and then by (ii) a second digit indicating the quadrant of the globe in which the quadrangle is located.

More detail here: http://www.fao.org/fishery/cwp/handbook/G/en