Aligning nodes to center in \tikz

Question

I'm trying to create the following diagram:

          |Welcome|
|Low|                   |High|

         |Truth|

          |Lie|

So far, this is what I've come up with:

The idea is that the node Welcome is in the center of the page, with Low and High on either sides of it. Then, the nodes Truth and Lie should be in the center of the page again.

This is my MWE:

\documentclass[11pt]{report}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric, arrows}
\usepackage{pgfplots}

\begin{document}

\tikzstyle{comp1} = [draw, rectangle, rounded corners, minimum height=1cm, minimum width=4cm, fill=gray!50]
\tikzstyle{comp2} = [draw, rectangle, rounded corners, minimum height=1cm, minimum width=4cm]
\tikzstyle{comp3} = [draw, ellipse, minimum height=1cm, minimum width=4cm, fill=gray!10, text centered]

\tikzstyle{arrow} = [thick,->,>=stealth]

\begin{figure}
\centering

\begin{tikzpicture}[node distance=2cm]
%%% NODES %%%
\node (welcome)     [comp1]                             {Welcome};

\node (low)         [comp2, below of=welcome]           {Low};
\node (high)        [comp2, right of=low, xshift=3cm]   {High};
\node (truth)       [comp3, below of=low]               {Truth};
\node (lie)         [comp3, below of=truth]             {Lie};

%%% ARROWS %%%
\draw [arrow] (welcome) -- (low);
\draw [arrow] (welcome) -- (high);
\draw [arrow] (low) -- (truth);
\draw [arrow] (high) -- (truth);
\draw [arrow] (truth) -- (lie);
\end{tikzpicture}
\end{figure}

\end{document}

I'm aware that this might have a simple solution, but I can't seem to find it, even after googling around. So, can anyone help?

Answer 1

You can add an coordinate below of=welcome and then use it as reference:

\documentclass[tikz,border=10pt]{standalone}
\usetikzlibrary{shapes.geometric, arrows}

\begin{document}

\tikzstyle{comp1} = [draw, rectangle, rounded corners, minimum height=1cm, minimum width=4cm, fill=gray!50]
\tikzstyle{comp2} = [draw, rectangle, rounded corners, minimum height=1cm, minimum width=4cm]
\tikzstyle{comp3} = [draw, ellipse, minimum height=1cm, minimum width=4cm, fill=gray!10, text centered]

\tikzstyle{arrow} = [thick,->,>=stealth]

\begin{figure}
\centering

\begin{tikzpicture}[node distance=2.2cm]
%%% NODES %%%
\node (welcome)     [comp1]                 {Welcome};
\coordinate[below of=welcome] (c);
\node (low)         [comp2, left of=c]      {Low};
\node (high)        [comp2, right of=c]     {High};
\node (truth)       [comp3, below of=c]     {Truth};
\node (lie)         [comp3, below of=truth] {Lie};

%%% ARROWS %%%
\draw [arrow] (welcome) -- (low);
\draw [arrow] (welcome) -- (high);
\draw [arrow] (low) -- (truth);
\draw [arrow] (high) -- (truth);
\draw [arrow] (truth) -- (lie);
\end{tikzpicture}
\end{figure}

\end{document}

Update

Some "standard" improvements as suggested by Gonzalo Medina:

• below=of welcome instead of below of=welcome
• or (if you like) more precise below=2.4cm of welcome
• \tikzset (new syntax) instead of \tikzstyle (old syntax)

Related: Should \tikzset or \tikzstyle be used to define TikZ styles?

\documentclass[tikz,border=10pt]{standalone}
\usetikzlibrary{positioning}
\usetikzlibrary{shapes.geometric, arrows}

\begin{document}

\tikzset{
    comp1/.style={draw, rectangle, rounded corners, minimum height=1cm, minimum width=4cm, fill=gray!50},
    comp2/.style={draw, rectangle, rounded corners, minimum height=1cm, minimum width=4cm},
    comp3/.style={draw, ellipse, minimum height=1cm, minimum width=4cm, fill=gray!10, text centered},
    arrow/.style={thick,->,>=stealth}
}

\begin{figure}
\centering

\begin{tikzpicture}[node distance=2cm and 1cm]
%%% NODES %%%
\node [comp1]                 (welcome) {Welcome};
\coordinate[below=of welcome] (c);
\node [comp2, left=of c]      (low)     {Low};
\node [comp2, right=of c]     (high)    {High};
\node [comp3, below=of c]     (truth)   {Truth};
\node [comp3, below=of truth] (lie)     {Lie};

%%% ARROWS %%%
\draw [arrow] (welcome) -- (low);
\draw [arrow] (welcome) -- (high);
\draw [arrow] (low)     -- (truth);
\draw [arrow] (high)    -- (truth);
\draw [arrow] (truth)   -- (lie);
\end{tikzpicture}
\end{figure}

\end{document}