TikZ: Problems with relative position

Question

I have a problem using relative positioning in TikZ. As shown in the MWE below, my "vertex circles" are not placed correctly when putting two figures side by side using \node[right = of ...] syntax.

Code using "right = of ..." syntax:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}

\tikzset{
    vertex/.style={circle,fill=black,minimum size=.8mm,inner sep=0pt}
}

\begin{document}
\begin{tikzpicture}
\node (2nd_1) at (0,0) {
    \tikz{
        \coordinate (u1) at (0,0);
        \coordinate[below= of u1] (l1);
        \coordinate[right= of u1] (u2);
        \coordinate[right= of l1] (l2);
        %           
        \draw           (u1)    --  (l1);
        \draw           (u2)    --  (l2);
        \draw           (l1)    --  (l2);
        \draw           (l1)        node[vertex]{};
        \draw           (l2)        node[vertex]{};
    }
};
\node[right=0 of 2nd_1] (2nd_2) {
    \tikz{
        \coordinate (u1) at (0,0);
        \coordinate[below= of u1] (l1);
        \coordinate[right= of u1] (u2);
        \coordinate[right= of l1] (l2);
        %           
        \draw           (u1)    --  (l1);
        \draw           (u2)    --  (l2);
        \draw           (l1)    --  (l2);
        \draw           (l1)        node[vertex]{};
        \draw           (l2)        node[vertex]{};
    }
};
\end{tikzpicture}
\end{document}

Code setting the position manually:

\begin{tikzpicture}
\node (2nd_1) at (0,0) {
    \tikz{
        \coordinate (u1) at (0,0);
        \coordinate[below= of u1] (l1);
        \coordinate[right= of u1] (u2);
        \coordinate[right= of l1] (l2);
        %           
        \draw           (u1)    --  (l1);
        \draw           (u2)    --  (l2);
        \draw           (l1)    --  (l2);
        \draw           (l1)        node[vertex]{};
        \draw           (l2)        node[vertex]{};
    }
};
\node (2nd_2) at (1.5,0) {
    \tikz{
        \coordinate (u1) at (0,0);
        \coordinate[below= of u1] (l1);
        \coordinate[right= of u1] (u2);
        \coordinate[right= of l1] (l2);
        %           
        \draw           (u1)    --  (l1);
        \draw           (u2)    --  (l2);
        \draw           (l1)    --  (l2);
        \draw           (l1)        node[vertex]{};
        \draw           (l2)        node[vertex]{};
    }
};
\end{tikzpicture}

Left: using "right = of" syntax. Right: Manual position

As is evident from the picture, the vertex-circles are not placed correctly on the second figure to the left. I can't seem to figure out, where the error originates so any help/explanation is appreciated.

Answer 1

Another case study of the message: Don't nest tikzpictures! The \tikz{} contents inherit the node options due to being in the same scope hence it doesn't start a fresh copy of tikzpicture environment.

If you want to group things together use scopes and shift the scope.

\documentclass[tikz]{standalone}
\usetikzlibrary{positioning}
\tikzset{vertex/.style={circle,fill=black,minimum size=.8mm,inner sep=0pt}}

\begin{document}
\begin{tikzpicture}
        \coordinate (u1) at (0,0);
        \coordinate[below= of u1] (l1);
        \coordinate[right= of u1] (u2);
        \coordinate[right= of l1] (l2);
        %           
        \draw           (u1)    --  (l1);
        \draw           (u2)    --  (l2);
        \draw           (l1)    --  (l2);
        \draw           (l1)        node[vertex]{};
        \draw           (l2)        node[vertex]{};

\begin{scope}[shift={([xshift=1cm]u2)}]
        \coordinate (u1) at (0,0);
        \coordinate[below= of u1] (l1);
        \coordinate[right= of u1] (u2);
        \coordinate[right= of l1] (l2);
        %           
        \draw           (u1)    --  (l1);
        \draw           (u2)    --  (l2);
        \draw           (l1)    --  (l2);
        \draw           (l1)        node[vertex]{};
        \draw           (l2)        node[vertex]{};
\end{scope}
\end{tikzpicture}
\end{document}