From GISWiki

Generic Mapping Tools (GMT) is an open source collection of ~60 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. GMT supports ~30 map projections and transformations and comes with support data such as 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.

Weblinks

• http://gmt.soest.hawaii.edu/
• Homepage
• Interactive online map generation using GMT
• Some examples
• iGMT: a graphical front-end for GMT
• Online Map Creation - an invaluable web implementation of GMT

An example of a map created with GMT, illustrating the empire of Alexander the Great