\begin{tikzpicture}[scale=1.5]
              \fill[color=blue!10](0,0) rectangle (1,1);
              \foreach \x in {-1,0,1,2} {\draw (\x,-1.2)--(\x,2.2); \draw (-1.2,\x)--(2.2,\x);}
              \foreach \x in {-.4,.6,1.6} \foreach \y in {-.1,.9,1.9} {\tkzDrawPoint[fill=red](\x,\y)}
              \foreach \x in {-.8,.2,1.2} \foreach \y in {-.9,.1,1.1} {\tkzDrawPoint[fill=blue](\x,\y)}
              \draw[dashed] (.6,.9)--(.2,1.1);
              \draw[dashed] (.6,-.1)--(.2,.1);
              \draw (-.4,-.1) node[below]{\(z\)};
              \draw (-.8,.1) node[above]{\(w\)};
              \clip (0,0) rectangle (1,1);
              \draw[thick,color=blue] (.6,.9)--(.2,1.1);
              \draw[thick,color=blue] (.6,-.1)--(.2,.1);
              \draw (.6,.9) node[below]{\([u]\)};
              \draw (.2,.1) node[above]{\([v]\)};
              \tkzDrawPoint[fill=red](.6,.9)
              \tkzDrawPoint[fill=blue](.2,.1)
              \end{tikzpicture}