Wikipedia
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.).