Contour plot can be make for the case z=f(x,y) For example, Electronic dispersion of a two dimensional graphite plane ( graphene) can be a good example of a contour plot. for details please read the book 'Physical Properties of Carbon Nanotube' by R. Saito, G Dresselhaus, M S Dresselhaus (Imperial Press).
Gnuplot can make figure from dat ( example: graphene.dat) format file. following are the script to make a contour plot of Electronic dispersion of graphene
please set your own x,y range and x,y label
to make the surface square
How to save the gnuplot figure
1. To save the figure in png format
2. To save the figure in eps format
3. To save as pdf format
(Tareque)