I am creating a flowchart using Tikz. Where under the main block, three blocks will share the equal space. I have tried with this
\documentclass[11pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usetikzlibrary{shapes, shadows, arrows, positioning}
\begin{document}
\tikzstyle{decision} = [diamond, draw]
\tikzstyle{line}= [draw,-latex',thick]
\tikzstyle{block}= [draw, rectangle,fill=gray!20, text width= 15em, minimum
height=15mm,text centered, node distance = 8 em]
\tikzstyle{block_c}= [draw, rectangle,fill=gray!20, text width= 10em,
minimum height=15mm,text centered, node distance = 8 em]
\begin{tikzpicture}
\node[block](A){xxx};
\node[block_c][below of =A](Data_c){Data collection feature};
\node[block_c][left of =Data_c,xshift=-80](B){Data collection feature};
\node[block_c][right of =Data_c,xshift=80](D){Data collection feature};
\end{tikzpicture}
\end{document}
But problem is that, the whold flowchart is not center of the page(i.e., there is a huge space on the left side). Is there anyway to fix this problem?


