\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}

\usepackage{tkz-fct}
\usetikzlibrary{arrows, decorations.pathreplacing}
\usetikzlibrary{shapes.misc}

\tikzset{
    line/.style={
        very thick,
        black,
        to path={% works only with "to" and not "--"
            -- (\tikztotarget) node[at start,point] {} node [at end,point] {} \tikztonodes
        }
    },
    point/.style={
        thick,
        draw=gray,
        cross out,
        inner sep=0pt,
        minimum width=4pt,
        minimum height=4pt,
    },
}

\begin{document}
\begin{preview}
\begin{tikzpicture}
       \draw[white,fill=white] (-1,-1) rectangle (22,8); % background
       \tkzInit [xmin=0,xmax=21,ymin=0,ymax=7]
        \begin{scriptsize}
            \tkzGrid[color = gray!30!white]
            \tkzAxeXY
        \end{scriptsize}
        \draw[line] (1,4) to (6,1);
        \draw[line] (2,1) to (5,4);
        \draw[line] (3,1) to (6,4);
        \draw[line] (4,1) to (8,5);
        \draw[line] (3,4) to (9,3);
        \draw[line] (7,2) to (9,3);
        \draw[line] (6,7) to (9,1);

        \draw[line] (11,1) to (16,5);
        \draw[line] (13,2) to (14,2);
        \draw[line] (14,1) to (14,2);
        \draw[line] (14,3) to (15,2);
        \draw[line] (15,4) to (15,3);
        \draw[line] (13,4) to (13,3);

        \draw[line] (17,3) to (21,3);
        \draw[line] (19,1) to (19,5);
\end{tikzpicture}
\end{preview}
\end{document}