[Tex/LaTex] TikZ parallel Edges between Nodes

tikz-pgf

I'm looking for a simple way to draw the following picture using TikZ. Namely, I would like to only specify the coordinates of the cities and then to connect them by edges using a \foreach loop. This would be easy if there were no directed edges at this picture:

enter image description here

So, more precisely, my question is how to modify the second \foreach below to get a picture above.

\begin{scope}
\foreach \x/\y/\name/\label/\where in {1.2/1.4/a/{El Paso}/below,     
   1/3.2/b/Albuquerque/above, 2.5/3/c/Amarillo/below, 3.8/4/d/Wichita/above,  
   4.3/3.3/e/Tulsa/45, 5.2/2.8/f/{Little Rock}/right, 4.2/2/g/Dallas/left, 
   4.8/1/h/Houston/right, 3.6/0.6/i/{San Antonio}/below} {
  \draw (\x,\y) circle (.4mm);
\node[draw,circle,minimum size=2mm,inner sep=0mm,label=\where:{\footnotesize \label}] (\name) at (\x,\y) {};
}

\foreach \s/\t in {a/b, b/c, c/e, e/d, e/f, f/g, h/g, h/i}
  \path[draw] (\s) edge (\t);
\end{scope}

Best Answer

If you create a simple "decoration" which simply draws a stroke from the initial to the final point, you can use the raise option for decorated paths to get a parallel path. Applying shorten > and shorten < to this raised path, and putting arrow tips on it, you get the desired result:

Result

Here is the code (the style parallel arrow takes care of all):

\documentclass{article}
\usepackage{tikz}
\begin{document}
\usetikzlibrary{decorations}
\pgfdeclaredecoration{sl}{initial}{
  \state{initial}[width=\pgfdecoratedpathlength-1sp]{
     \pgfmoveto{\pgfpointorigin}
  }
  \state{final}{
     \pgflineto{\pgfpointorigin}
    }
}

\tikzset{parallel arrow/.style={->, 
     shorten >=2mm, shorten <=2mm, 
     decoration={sl,raise=1mm},decorate}}

\begin{tikzpicture}
\begin{scope}
\foreach \x/\y/\name/\label/\where in {1.2/1.4/a/{El Paso}/below,     
   1/3.2/b/Albuquerque/above, 2.5/3/c/Amarillo/below, 3.8/4/d/Wichita/above,  
   4.3/3.3/e/Tulsa/45, 5.2/2.8/f/{Little Rock}/right, 4.2/2/g/Dallas/left, 
   4.8/1/h/Houston/right, 3.6/0.6/i/{San Antonio}/below} {
  \draw (\x,\y) circle (.4mm);
\node[draw,circle,minimum size=2mm,inner sep=0mm,label=\where:{\footnotesize \label}] (\name) at (\x,\y) {};
}

\foreach \s/\t in {a/b, b/c, c/e, e/d, e/f, f/g, h/g, h/i} {
  \path[draw] (\s) edge (\t);
  \path[draw] (\s) edge[parallel arrow] (\t);
  \path[draw] (\t) edge[parallel arrow] (\s);}
\end{scope}
\end{tikzpicture}
\end{document}

Update

I added the numbers in each route. I had some fun parametrizing their position so that they can be all put in a single loop.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,calc}
\begin{document}
\pgfdeclaredecoration{sl}{initial}{
  \state{initial}[width=\pgfdecoratedpathlength-1sp]{
     \pgfmoveto{\pgfpointorigin}
  }
  \state{final}{
     \pgflineto{\pgfpointorigin}
    }
}
\tikzset{parallel arrow/.style={latex-,
     shorten >=2mm, shorten <=2mm, 
     decoration={sl,raise=1mm},decorate}}

\begin{tikzpicture}
\begin{scope}
\foreach \x/\y/\name/\label/\where in {1.2/1.4/a/{El Paso}/below,     
   1/3.2/b/Albuquerque/above, 2.5/3/c/Amarillo/below, 3.8/4/d/Wichita/above,  
   4.3/3.3/e/Tulsa/45, 5.2/2.8/f/{Little Rock}/right, 4.2/2/g/Dallas/left, 
   4.8/1/h/Houston/right, 3.6/0.6/i/{San Antonio}/below} {
  \draw (\x,\y) circle (.4mm);
\node[draw,circle,minimum size=2mm,inner sep=0mm,label=\where:{\footnotesize \label}] (\name) at (\x,\y) {};
}

\tikzset{edge label/.style={font=\tiny, inner sep=1.6mm},
ab/.style={edge label, left},
ba/.style={edge label, right},
bc/.style={edge label, above},
cb/.style={edge label, below},
ce/.style={bc},
ec/.style={cb},
ed/.style={ab},
de/.style={ba},
ef/.style={edge label, below left, inner sep=1mm},
fe/.style={edge label, above right, inner sep=1mm},
fg/.style={edge label, above left, inner sep=1mm},
gf/.style={edge label, below right, inner sep=1mm},
hg/.style={ab},
gh/.style={ba},
hi/.style={bc},
ih/.style={cb}
}  

\foreach \s/\t/\from/\to in {a/b/9/10, b/c/8/11, c/e/7/12, e/d/6/5, 
                             e/f/13/4, f/g/14/3, h/g/15/2, h/i/16/1} {
  \path[draw] (\s) edge (\t) ($(\s)!.5!(\t)$) node[\s\t] {\from} node[\t\s]{\to};
  \path[draw] (\s) edge[parallel arrow] (\t);
  \path[draw] (\t) edge[parallel arrow] (\s);
}
\end{scope}
\end{tikzpicture}
\end{document}

Result

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