# set terminal pngcairo  transparent enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'contourfill.4.png'
set key title "&{----} z = x^2 + y^2(1-x)^3" enhanced   center
set key inside right top vertical Right reverse enhanced autotitle nobox
set key noinvert samplen 0.1 spacing 1 width 0 height 0
set view map scale 1
set samples 51, 51
set isosamples 51, 51
set contour base
set cntrlabel onecolor format '%8.3g' font '' start 5 interval 20
set cntrparam cubicspline
set cntrparam levels 9
set cntrparam levels incremental -20,5
set contourfill cbtics
set xyplane relative 0
set xtics border in scale 0,0 nomirror norotate  autojustify
set ytics border in scale 0,0 nomirror norotate  autojustify
set ztics border in scale 0,0 nomirror norotate  autojustify
set cbtics border in scale 0,0 mirror norotate  autojustify
set cbtics  norangelimit -20.0000,5 ,20.0000
set rtics border in scale 0,0 nomirror norotate  autojustify
set title "set view map;   splot with contourfill + contour lines" 
set xrange [ -1.00000 : 5.00000 ] noreverse
set yrange [ -3.00000 : 3.00000 ] noreverse
set zlabel "Z " 
set zlabel  offset character 1, 0, 0 font "" textcolor lt -1 norotate
set zrange [ -25.0000 : 25.0000 ] noreverse
set cbrange [ -21.0000 : 21.0000 ] noreverse
set lmargin at screen 0
set bmargin at screen 0
set pm3d interpolate 1,1 flush begin noftriangles border retrace linewidth 1.000 dashtype solid corners2color mean
set palette positive nops_allcF maxcolors 0 gamma 1.5 viridis
unset colorbox
f(x,y) = sinc( sqrt(x*x + y*y) )
g(x,y) = x**2 + y**2 * (1 - x)**3
NO_ANIMATION = 1
splot g(x,y) with contourfill fs solid border notitle,       g(x,y) nosurface lt black title "Contour levels Δz = 5"