Making an image plot or heat map

The information that is presented in a planar contour plot can also be conveyed by coloring or shading the x-y plane, rather than by drawing contours on it. The resulting graph is called an image plot, or sometimes, a heat map:

Depending on the character of the data to be plotted and the features one wants to call attention to, and to some extent the physical characteristics of the output device, either a contour plot or an image plot might be preferred.

How to do it…

The previous figure was created using the following script:

set xrange [-4:4]
set yrange [-4:4]
set iso 100
set samp 100
unset key
unset sur
set view map
set pm3d at b
splot sin(y**2+x**2) - cos(x**2)

How it works…

Let's look at the highlighted code line first. This set pm3d line, which we used at the beginning of the chapter to plot surfaces, here has the additional clause at b, which means at bottom. This says to draw the data color map on the x-y plane rather than on the surface itself. The...