C-squares

C-squares (acronym for the concise spatial query and representation system) is a system of geocodes (actually a type of global grid) that provides a basis for simple spatial indexing of geographic features or data. It was devised by Tony Rees of CSIRO Marine and Atmospheric Research (then "CSIRO Marine Research") in 2001-2, and described in the literature in 2003. The notation system of c-squares incorporates a compact encoding of latitude and longitude coordinates into a machine- and human-readable c-squares code, which can then be used either for spatial search or display via a suitable mapping application. The c-squares codes also provide an application- and vendor-independent, interoperable notation system for any gridded data whose units of organization correspond with steps of the c-squares hierarchy (e.g. 5-, 1-, 0.5 degree cells, etc.).

According to the initial system description, c-squares was devised as an improved (more precise) method for expressing dataset geographic extents in searchable metadata catalogues, in place of (or in addition to) conventional bounding rectangle representations. The method is also useful as a generic, interoperable notation for gridded data (see above), for example a variety of datasets that describe environmental characteristics of global half-degree cells (see AquaMaps site). C-squares can also simply be used for mapping (example: CSIRO Marine and Atmospheric Research's "CAAB" application), although the most value is obtained when the system is used for spatial search as well (e.g. OBIS database, CMAR's "MarLIN" metadatabase, etc.).

C-squares provides a hierarchical nomenclature for dividing 10°x10° World Meteorological Organization (WMO) squares into smaller units (each an individual "c-square") of 5°x5°, 1°x1°, 0.5°x0.5°, 0.1°x0.1°, etc., using an alternating base 2, base 5 linear division, as fine as may be required. Each cell of the resulting subdivision is allocated a unique alphanumeric identifier (c-squares code), such that the position of an object or objects on the surface of the Globe can be represented by a set of one or more such codes that define the cell(s) within which the object occurs. Storing these codes as text identifiers, for example in a database, repository of spatial metadata, searchable text file or web page, then offers the functionality for a simple, text-based spatial search, without the requirement for any more complex geographic information system (GIS). Once stored (or if desired, generated on-the-fly using a c-squares encoder), a code or set of codes can also be rendered on a map by a utility (for example, the web-accessible c-squares mapper) that incorporates the relevant decoding routines.

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