The CSIRO Marine and Atmospheric Research (CMAR) c-squares mapper is a web utility which plots dataset exents on a range of base maps, according to a string of c-squares (unique identifiers for global grid squares) passed to it via the web. Technical details of how to do this are available here. A range of user-selectable base maps are available, including maps based on USGS/NASA JPL data and the U.S. National Geophysical Data Center/NOAA GLOBE project. The mapper code and associated c-squares encoding routines were developed by Tony Rees, Miroslaw Ryba and Philip Bohm at CMAR in Australia, and are available as open source via the c-squares project page at http://sourceforge.net/ projects/csquares/. For additional information on c-squares spatial indexing and mapping, visit the c-squares home page.