Plotting in FORTRAN (and other common programming languages) can easily be done using for e.g. DISLIN a "A Data Plotting Library" (
(Max Planck Institute for Solar System Research)
"...DISLIN is a high-level and easy to use plotting library for displaying data as curves, bar graphs, pie charts, 3D-colour plots, surfaces, contours, and maps. The library contains about 500 plotting and parameter setting routines. The approach used is to have only a few graphics routines with short parameter lists. A large variety of parameter setting routines can then be used to create customized graphics. Several output formats are supported such as X11, VGA, PostScript, PDF, SVG, CGM, HPGL, TIFF, GIF, PNG and BMP. DISLIN is available for the programming languages C, Fortran 77, Fortran 90, Perl, Python and Java..."
You don't need a DISLIN license for a non-commercial use of DISLIN, otherwise a licence is available for low price.