set contour s
unset surface
set pm3d map nohidden3d
set cntrparam level incr -8,1,10 
f(x,y) = 3*(1-x)**2*exp(-x**2 - (y+1)**2)\
        - 10*(x/5.0 - x**3 - y**5)*exp(-x**2 - y**2)\
        - exp(-(x+1)**2 - y**2)/3
set palette rgbformulae 5,7,15
set samples 100
set isosamples 100
unset key
set label "{/Helvetica=18 pm3d map (contour,set)}" at sc 0.15,0.92
set term pngcairo enh font "Times,10" size 480,480
set out "pm3dmap_unset_surface.png"
splot [-3:3][-3:3] f(x,y) w pm3d