The GCONTOUR procedure requires three
numeric variables to produce a plot. The input data set forms a rectangular
grid from the values of
x and
y.
The
z variable is plotted on
the grid as the third dimension. Only one value of
z is
required for each
(x,y) grid
location. If multiple observations have the same
z value
for any
(x,y) combination,
only the last observation is plotted.