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, Walter H. F. Smith, Remko Scharroo, Joaquim Luis, and Florian Wobbe, with help from a global set of volunteers, and is supported by the National Science Foundation. It is released under the GNU Lesser General Public License.

GMT is used all over the world. Each yellow dot represent a 15x15 arc minute block with one or more registered user or institution. So far, almost 2000 such blocks have been registered, representing more than 15,000 individual GMT users. To add your dot, fill out the registration form.