OzAPI is source code that enables user interfaces to be developed and graphics output to be designed for FORTRAN and 'C' programs using Tcl/Tk libraries.
An example fortran program is supplied which you would normally use as a starting point for your application.
The GUI is usually menu driven, and there are various dialogs that can be used.
Graphics are based on the GKS graphics standard for drawing text, lines polygons etc
Code extracted from the OzGIS mapping system.