Geographic classification systems

A geographic classification system can be defined as a way of grouping and organizing geographic references (reference points, lines or areas) to be used as reference data for geo-referencing statistical datasets. To facilitate its use, a geographic classification system is generally complemented by a coding system (refer below) for the elements that compound the classification. A geographic classification system can be hierarchical (e.g. nested areas, grid cells with various resolutions) or not. It may also be time-dependent (e.g. change of area boundaries over time).

Different types of geographic classification systems can be distinguished such as:

• Irregular area classification systems: Systems where the elements correspond to irregular areas. e.g.
  • Countries or areas
  • FAO Major Fishing Areas for Statistical Purposes
  • Exclusive Economic Zones
  • Regional Fishery Bodies Competence areas
  • Reporting areas, Fishing zones.

• Grid classification systems: System defined by a regular geo-referenced grid characterized by
  • a maximum geographic extent or scale (global, regional, local)
  • a grid unit/cell shape (e.g. square, rectangle)
  • a grid resolution (e.g. 1 x 1degree, 5 x 5 degree)

• Linear classification systems: System defined by elements characterized by a linear shape, e.g. haul trajectory.

• Locations: System defined by elements characterized by points (locations), e.g. landing site.

Geographic coding systems

Geographic coding systems are recommended to facilitate the use of geographic classification systems and the geo-referencing of fisheries statistics. A geographic coding system consists in identifying each element of the classification with a unique, permanent and meaningful code (generally in the form of a combination of text elements and numbers). Depending on the purpose and nature of the geographic classification, the way to build the identifiers will differ. Coding system conventions for the main irregular area classification systems of interest to fisheries are described in the relevant classification systems (above).

Grid coding systems

A grid coding system can be defined as the logic associated to a grid classification system that allows converting a pair of geographic coordinates (longitude/latitude) into a string-based code, and vice-versa. In the computing field, coding will mean both encoding (to obtain a grid cell code from a pair of geographic coordinates) and decoding (obtain the geographic coordinates - center - for a given grid cell code). For a same grid classification system, there can be different mechanisms to encode/decode, i.e. different grid coding systems.

• Areal grid coding system - Recognizing the need for areal breakdown, the CWP has recommended the use of a global coding system (refer areal grid system)

• Other grid coding systems - For the purpose of fisheries data reporting where square-based grids are used, other alternative grid coding systems can be used, as long as they are compatible with the above CWP areal grid coding system and facilitate the implementation of grid coding systems by fisheries management organization. The C-Square coding system (CSIRO, Australia) provides an alternative coding system which is compatible with the CWP areal grid coding system  from the 10 degree x 10 degree resolution to smaller resolutions, and provides a coding mechanism solution for small scales where the areal grid coding system is limited to a minimum resolution 10 minutes x 10 minutes.

FAO. FAO Major Fishing Areas. [Cited 1 November 2020]. https://www.fao.org/fishery/en/area/search/en

FAO. List of countries or areas. [Cited 1 November 2020]. https://www.fao.org/3/bt978e/bt978e.pdf

FAO. Regional Fishery Bodies (area of competence). [Cited 1 November 2020]. https://www.fao.org/fishery/en/collection/organization

Rees, T. 2003. C-Squares, a new spatial indexing system and its applicability to the description of oceanographic datasets. Oceanography 16(1): 11-19. (also available at http://www.cmar.csiro.au/csquares/).