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.1

Description

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.2

Examples of dataset footprints displayed using C-squares.3

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, for example a variety of datasets that describe environmental characteristics of global half-degree cells. 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., … 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).4

The CMAR c-squares mapper is a perl utility which plots dataset extents (geographic footprints) on a range of base maps, according to a string of c-squares (and optional other parameters) passed to it via the web.5

 The system was developed by Dr Tony Rees of CSIRO Marine and Atmospheric Research (CMAR) in 2001-2002 and is freely available for use worldwide without royalty or licence.

Function

• Visualisation tools
  • Maps

Why use this tool?

• To create searchable metadata
• For displaying a range of types of complex dataset footprints6

 Who will use this tool?

• Data capture
  • Curators
• Data providers
  • Institutions
  • Private collections
• Data users
  • Expert
  • Interest groups
• ALA infrastructure

 How will the tool be used?

• Lat/long/c-squares converter is available online and as an Excel spreadsheet
• C-squares mapper is a web-accessible, perl based utility
• Installations of the c-squares mapper at CMAR currently run on UNIX and SUSE Linux and the mapper and Xmapper have also been successfully installed and run on Windows servers.7
• Hardware requirements: web server capable of running cgi programs8
• Software requirements: Apache or equivalent web server, Perl, CGI for Perl9

 Where in the data chain could this tool be used?

• The c-squares mapper and lat/long converter would  sit on a server and be accessed through a user’s machine

 When could this tool be used?

• At the time of a user request
• As a post process, after data is with the user

Availability

• C-squares: http://www.marine.csiro.au/csquares/
• C-squares FAQ: http://www.marine.csiro.au/csquares/csq-faq.htm
• C-squares mapper code: http://sourceforge.net/project/showfiles.php?group_id=158386
• Lat/long converter: http://sourceforge.net/project/showfiles.php?group_id=158386
• Free to use. No royalty or licence.

Comments

C-squares use latitudes and longitudes as a reference, and so:

• They are not square (In the southern hemisphere, the southern boundary will be shorter than the northern boundary.)
• The size of a c-square will change with a change in latitude.

  See FAQ 16 How big (and what shape) are individual c-squares on the ground?