[1] The individual rectangles that make up the system each measure 1 degree of longitude by 0.5 degrees of latitude and are intended to be roughly square in real world use in the ICES region of interest, approximately 30 nautical miles by 30 nautical miles (55×55 km) at 60°N, although the actual width varies with latitude, gradually becoming wider than they are high south of 60°N, and narrower further north.
The resulting grid is 113 columns by 99 rows, comprising 11,187 labelled 1×0.5 degree cells.
[2][3] The grid covers both land and sea areas across its designated region, but as per the interests of its originating body, is typically employed for use with marine data such as analysis of marine resources, fishing activities, seabed habitat, etc., refer example references below.
[4] To accommodate the visualization and/or analysis of finer scale data than is supported by the "standard" (1×0.5 degree) rectangles, an optional fifth character (as digits 1 through 9) can be used which will place a location within a finer 9-cell (3 by 3) sub-grid, for which the individual sub-rectangles then measure 20' of longitude by 10' of latitude (approximately 10×10 nautical miles).
[2] ICES rectangles have been used for reporting and analysis in numerous marine publications since the 1970s; for recent examples see.