GMT is an open source collection of ~65 tools for manipulating geographic and Cartesian data sets (including filtering, trend fitting, gridding, projecting, etc.) and producing Encapsulated PostScript File (EPS) illustrations ranging from simple x-y plots via contour maps to artificially illuminated surfaces and 3-D perspective views; the GMT supplements add another ~70 more specialized tools. GMT supports over 30 map projections and transformations and comes with support data such as GSHHS coastlines, rivers, and political boundaries. GMT is developed and maintained by Paul Wessel and Walter H. F. Smith with help from a global set of volunteers, and is supported by the National Science Foundation. It is released under the GNU General Public License.

GMT is used all over the world. Each yellow dot represent a 15x15 arc minute block with one or more registered users or institutions. So far, over 2100 such blocks have been registered, representing more than 25,000 individual GMT users. To add your dot, fill out the registration form.

GMT celebrated its 20th anniversary on Oct 7, 2011. The event was marked by a seminar at the University of Hawaii where Paul Wessel gave a talk on the origin, use, capabilities, and future of GMT. For a 540p video podcast of the presentation [47 minutes; 247 Mb], visit iTunes University or download the MP4 video directly from here.