\documentclass{article}
\usepackage{pstricks,pst-node}
\usepackage{amsmath}
\usepackage{amsfonts}
% used for planning pspictures
\newpsobject{showgrid}{psgrid}{subgriddiv=1,griddots=10,gridlabels=6pt}
\begin{document}
\pagestyle{empty}
\psset{unit=1.5cm}
\begin{pspicture}(-1.5,-1.5)(1.5,1.5)%\showgrid
\psline[linecolor=gray,linestyle=dashed](-1.5,0)(1.5,0)
\psline[linecolor=gray,linestyle=dashed](0,-1.5)(0,1.5)
\psdots[dotstyle=o,dotscale=1.5](-1,-1)(-1,1)(1,1)(1,-1)
\psline[linecolor=black,linestyle=solid](-1,-1)(-1,1)
\psline[linecolor=black,linestyle=solid](-1,-1)(1,-1)
\psline[linecolor=black,linestyle=solid](-1,1)(1,1)
\psline[linecolor=black,linestyle=solid](1,1)(1,-1)
\uput[dl](-1,-1){(-1,-1)}
\uput[ul](-1,1){(-1,1)}
\uput[dr](1,-1){(1,-1)}
\uput[ur](1,1){(1,1)}
\end{pspicture}
\end{document}