Images from a DEM viewer I wrote [inspired by Smitty]:
These are of the Grand Canyon.
Images from a function browser for functions of 3 variables:
These are isosurfaces of a scalar function F(x,y,z) = N
and are function mapped by Grad( F(x,y,z) )
f(x,y,z) = x^2 + y^2 + x*sin(x+y-z), f() = 4.0
f(x,y,z) = 0.5 * x * sin(1.2 * x^2) - 0.7 * y* (1.2+cos(1.8 * y^2)) - z, f() = 0