How to connect two lines in TikZ?

Question

I finally managed to draw the following path diagram with TikZ. Now, however, I am facing a challeging task. I would like to connect two edges/lines (here drawn in red; for the social scientists, I want to illustrate an interaction effect). How can I do that?

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{positioning,mindmap,trees,shapes,shadows,calc,arrows,automata,decorations.text}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}[grow=left,
  line/.style={>=latex},
  coef/.style={font=\tiny},
  rect/.style={font=\tiny, rectangle, draw, text width=.49cm, align=center, node distance = 1.8cm},
  mycircle/.style={font=\tiny, circle, draw,  node distance = 0.2cm},
  beschrif/.style={font=\tiny}]

  \node[rect] (stab) {$D$};

  \node[rect] (zuf_m) [above left = of stab] {$S_m$};
  \node[rect] (zuf_f) [below left = of stab] {$S_f$};

  \node[rect] (konf_m) [above left = of zuf_m] {$FoC_m$};
  \node[rect] (konf_f) [below left = of zuf_f] {$FoC_f$};

  \node[rect] (unemp_m) [below left= of konf_m] {$U_m$};
  \node[rect] (unemp_f) [above left= of konf_f] {$U_f$};

  \node[rect] (behav_m) [above = 0.6cm of zuf_m] {$CB_m$};
  \node[rect] (behav_f) [below = 0.6cm of zuf_f] {$CB_f$};

  \node (error_sm) [mycircle, right = 1.3cm of zuf_m] {$\epsilon_{Sm}$};
  \node (error_cm) [mycircle, right = 2.8cm of konf_m] {$\epsilon_{FoCm}$};

  \node (error_sf) [mycircle, right = 1.3cm of zuf_f] {$\epsilon_{Sf}$};
  \node (error_cf) [mycircle, right = 2.8cm of konf_f] {$\epsilon_{FocCf}$};

  \path (zuf_m.east) edge[->,line] (stab.west);
  \path (zuf_f.east) edge[->,line] (stab.west);

  \path (unemp_m.east) edge[->,line] (zuf_m.west);
  \path (unemp_f.east) edge[->,line] (zuf_f.west);
  \path (unemp_m.east) edge[->,line] (zuf_f.north west);
  \path (unemp_f.east) edge[->,line] (zuf_m.south west);

  \path (unemp_m.east) edge[->,line] (konf_m.west);
  \path (unemp_f.east) edge[->,line] (konf_f.west);
  \path (unemp_m.east) edge[->,line] (konf_f.north west);
  \path (unemp_f.east) edge[->,line] (konf_m.south west);

  \path (konf_m.east) edge[->,line] (zuf_m.north west);
  \path (konf_f.east) edge[->,line] (zuf_f.south west);

  \path (error_sm) edge[->, line] (zuf_m);
  \path (error_sf) edge[->, line] (zuf_f);

  \path (error_cm) edge[->, line] (konf_m);
  \path (error_cf) edge[->, line] (konf_f);

  \path (error_sm) edge[<->, bend left=90, line] (error_sf);
  \path (error_cm) edge[<->, bend left=90, line, looseness=1] (error_cf);

\end{tikzpicture}

\end{document}

Answer 1

You can use the calc tikzlibrary (which you already have included) to calculate a point on the line, i.e. between the two coordinates:

\draw[-latex,red] (behav_f.west) -- ($(konf_f.east)!0.6!(zuf_f.south west)$);

The value 0.6 gives the relative position between the two coordinates. You can adjust it to your needs.

Answer 2

Depending on what you want, either

1. simply place a coordinate along the path, the key pos (or one of its wrapper like at start) can be used to specify the position; or

2. if you want a specific angle, you can use intersection of (or the intersections library). The (left:1) is a special case of a polar coordinate which means the same as (180:1), of course you can use any angle. For a solution with the intersections library, you first need to name both paths:

   \draw[->,name path=pathA] (a.east) -- (c.west);
   \path[name path=pathB] (b.west) -- ++ (<angle>:2);
   

   and then you can find the intersection with

   \draw[->, name intersections={of=pathA and pathB}] (b.west) -- (intersection-1);
   

   If you don't want to guess the distance that is needed (with intersections, the paths must actually cross unlike the intersection of solution) you can use a rather big distance like 10 but wrap it inside the pgfinterruptboundingbox environment to ensure that the path doesn't interfere with your picture's bounding box.

Code

\documentclass[tikz,convert=false]{standalone}
\tikzset{nodes=draw,every edge/.append style={thick}}
\begin{document}
\begin{tikzpicture}
\node (a) {A};
\node (b) at (2,-1) {B};
\node (c) at (2,-2) {C};
\path[->] (a.east) edge coordinate[pos=.7] (ac) (c.west)
          (b.west) edge [shorten >=2\pgflinewidth] (ac);
\end{tikzpicture}

\begin{tikzpicture}
\node (a) {A};
\node (b) at (2,-1) {B};
\node (c) at (2,-2) {C};
\path[->] (a.east) edge (c.west)
          (b.west) edge [shorten >=2\pgflinewidth]
                      (intersection of a.east--c.west and b.west--[shift={(left:1)}]b.west);
\end{tikzpicture}
\end{document}

Answer 3

Beside previous answers, if you want your connections have a certain angle, you can use intersections library. You need two named paths: one will be the edge

\path (konf_m.east) edge[->,line,name path=a] (zuf_m.north west);

and the other will be defined with

\path[name path=aa] (behav_m.west)--++(-135:3cm);

The arrow from behav_m.west to previous path is drawn with

  \draw[red,name intersections={of=a and aa},->,line] (behav_m.west)--(intersection-1);

Complete code and result are:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{intersections,positioning,mindmap,trees,shapes,shadows,calc,arrows,automata,decorations.text}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}[grow=left,
  line/.style={>=latex},
  coef/.style={font=\tiny},
  rect/.style={font=\tiny, rectangle, draw, text width=.49cm, align=center, node distance = 1.8cm},
  mycircle/.style={font=\tiny, circle, draw,  node distance = 0.2cm},
  beschrif/.style={font=\tiny}]

  \node[rect] (stab) {$D$};

  \node[rect] (zuf_m) [above left = of stab] {$S_m$};
  \node[rect] (zuf_f) [below left = of stab] {$S_f$};

  \node[rect] (konf_m) [above left = of zuf_m] {$FoC_m$};
  \node[rect] (konf_f) [below left = of zuf_f] {$FoC_f$};

  \node[rect] (unemp_m) [below left= of konf_m] {$U_m$};
  \node[rect] (unemp_f) [above left= of konf_f] {$U_f$};

  \node[rect] (behav_m) [above = 0.6cm of zuf_m] {$CB_m$};
  \node[rect] (behav_f) [below = 0.6cm of zuf_f] {$CB_f$};

  \node (error_sm) [mycircle, right = 1.3cm of zuf_m] {$\epsilon_{Sm}$};
  \node (error_cm) [mycircle, right = 2.8cm of konf_m] {$\epsilon_{FoCm}$};

  \node (error_sf) [mycircle, right = 1.3cm of zuf_f] {$\epsilon_{Sf}$};
  \node (error_cf) [mycircle, right = 2.8cm of konf_f] {$\epsilon_{FocCf}$};

  \path (zuf_m.east) edge[->,line] (stab.west);
  \path (zuf_f.east) edge[->,line] (stab.west);

  \path (unemp_m.east) edge[->,line] (zuf_m.west);
  \path (unemp_f.east) edge[->,line] (zuf_f.west);
  \path (unemp_m.east) edge[->,line] (zuf_f.north west);
  \path (unemp_f.east) edge[->,line] (zuf_m.south west);

  \path (unemp_m.east) edge[->,line] (konf_m.west);
  \path (unemp_f.east) edge[->,line] (konf_f.west);
  \path (unemp_m.east) edge[->,line] (konf_f.north west);
  \path (unemp_f.east) edge[->,line] (konf_m.south west);

  \path (konf_m.east) edge[->,line,name path=a] (zuf_m.north west);
  \path (konf_f.east) edge[->,line,name path=b] (zuf_f.south west);

  \path (error_sm) edge[->, line] (zuf_m);
  \path (error_sf) edge[->, line] (zuf_f);

  \path (error_cm) edge[->, line] (konf_m);
  \path (error_cf) edge[->, line] (konf_f);

  \path (error_sm) edge[<->, bend left=90, line] (error_sf);
  \path (error_cm) edge[<->, bend left=90, line, looseness=1] (error_cf);

  \path[name path=aa] (behav_m.west)--++(-135:3cm);
  \path[name path=bb] (behav_f.west)--++(135:3cm);
  \draw[red,name intersections={of=a and aa},->,line] (behav_m.west)--(intersection-1);
  \draw[red,name intersections={of=b and bb},->,line] (behav_f.west)--(intersection-1);
\end{tikzpicture}

\end{document}