\documentclass[a4paper]{article}

\usepackage{pgfplots}

\begin{document}

\begin{tikzpicture}
	\begin{axis}[colormap/jet]
	\addplot[red,contour prepared={labels=false},contour prepared format=matlab] table
	{
	0 4
	0 0
	1 0
	0.5 0.5
	0 0
	0 4
	0 2
	1 2
	0.5 2.5
	0 2
	};
	\addlegendentry{contour}
	\end{axis}
\end{tikzpicture}
\end{document}

