
</DIV>

<H1>Contour Maps</H1>

In a contour map of <I>f</I>(<I>x,y</I>), the world-coordinates are
<I>x</I> and <I>y</I> and the contours are lines of constant <I>f</I>.
The PGPLOT contouring routines (<CODE>PGCONT</CODE> and
<CODE>PGCONS</CODE>) require the input data to be stored in a
two-dimensional Fortran array <CODE>F</CODE>, with element
<CODE>F(I,J)</CODE> containing the value of the function $f(x,y)$ for
a point $(x_i, y_j)$.  Furthermore, the function must be sampled on a
regular grid: the $(x,y)