Generic Mapping Tools (GMT) is a mature, open-source collection of approximately 100 command-line tools for processing geographic and Cartesian data and producing high-quality PostScript illustrations, maps, and animations. The system is architected as a modular C library with a central dispatcher executable (`gmt`) that loads and runs individual modules. It supports both a classic mode (direct module calls) and a modern mode (`gmt begin/end`, `gmt subplot`) that manages sessions, figures, and panels. Key entry points include the `gmt` command, the C API (`GMT_Create_Session`, `GMT_Call_Module`), and shell completion scripts. Data flows involve reading grid, table, image, and color palette table (CPT) data from local files or remote servers (via `@` prefix), processing through modules (e.g., `grdimage`, `psxy`, `grdmath`, `grdfilter`), and outputting PostScript, grids, or other formats. External dependencies include netCDF, GDAL, FFTW, PCRE/POSIX regex, PROJ, GSHHG coastlines, and DCW country polygons. The codebase exhibits high craftsmanship with systematic option parsing, a well-defined API, extensive test coverage, and reusable infrastructure components.