pop(x) = 103*exp((1965-x)/10) plot [1960:1990] 'population.dat', pop(x)
The file population.dat might contain:
# Gnu population in Antarctica since 1965 1965 103 1970 55 1975 34 1980 24 1985 10
A simple example of plotting a 3-d data file is
splot 'glass.dat'
where the file datafile.dat might contain:
# The valley of the Gnu. 0 0 10 0 1 10 0 2 10
1 0 10 1 1 5 1 2 10
2 0 10 2 1 1 2 2 10
3 0 10 3 1 0 3 2 10
Note datafile.dat defines a 4 by 3 grid ( 4 rows of 3 points each ). Rows are separated by blank lines.
Note also that the x value is held constant within each isoline. If you instead keep y constant, and plot with hidden-line removal enabled, you will find that the surface is drawn 'inside-out'.
Actually it is not necessary to keep the x values constant within an isoline, nor is it necessary to keep the y values the same along the perpendicular isolines. gnuplot requires only that the number of points be the same along each isoline.