documentclass[border=5mm]{standalone}
usepackage{pgfplots}
pgfplotsset{compat=1.13}
usepgfplotslibrary{colorbrewer}

begin{document}
begin{tikzpicture}[yscale=1]
begin{axis}[
domain=-180:180,
samples=50,
colormap/PiYG,
colorbar,
colorbar style={
    title=Color key,
    ylabel=Z-value,
    ytick={-1,-0.75,...,1},
    yticklabel style={
        text width=2.5em,
        align=right,
        /pgf/number format/.cd,
            fixed,
            fixed zerofill
        }
    }
]
addplot3 [surf] { cos(x)*cos(y) / 5};
end{axis}
end{tikzpicture}
end{document}