# Centering a text in longtable

I am having some difficulty with centering a text in a table. If you happen to have some spare time, please kindly enlighten me on the following problem.

Referring to the picture below, you could see that the word "Graph" is left aligned instead of center. How to make it centered? Could you please provide advice or guidance on the issue?

\documentclass{article}
\usepackage[english]{babel}
\usepackage{tikz}
\usepackage{multirow}
\usepackage{longtable}
\usepackage{booktabs}
\usepackage{array}

\newcommand{\tesplot}{%
\begin{tikzpicture}
[scale=.4,auto=center]
\node (n1) at (10.6,4.9) [draw, circle,fill=green!20] {1};
\node (n2) at (4,0.8) [draw, circle,fill=blue!20] {2};
\node (n3) at (3.8,11.4) [draw, circle,fill=green!20] {3};
\node (n4) at (0.1,6.4) [draw, circle,fill=green!20] {4};
\node (n5) at (3.6,3.4) [draw, circle,fill=blue!20] {5};
\node (n6) at (7.4,2.3) [draw, circle,fill=blue!20] {6};
\node (n7) at (9,10.4) [draw, circle,fill=green!20] {7};
\node (n8) at (18,10.8) [draw, circle,fill=green!20] {8};

\foreach \from/\to in {n6/n2,n2/n5,n5/n6}
\draw[blue] (\from) -- (\to);
\foreach \from/\to in {n1/n8,n8/n7,n7/n1,n3/n7,n4/n3}
\draw[green] (\from) -- (\to);
\foreach \from/\to in {n6/n1,n5/n4,n2/n4,n1/n5}
\draw[red] (\from) -- (\to);

\end{tikzpicture}
}
\begin{document}

\begin{longtable}{ l  l  l  l >{\centering\arraybackslash}m{7cm} }
\toprule
\multicolumn{5}{ c }{Convergence} \\
\midrule
Time & \multicolumn{2}{ c }{Information} & Graph & Description \\
\cmidrule(r){1-1}\cmidrule(lr){2-3}\cmidrule(lr){4-4}\cmidrule(l){5-5}
& Vertice & 8 & & \\[1cm]
1 & ${P(1)}$ & 0.5 &
\raisebox{-2.3cm}[50pt][50pt]{%
\tesplot} &  \raisebox{-0.1cm}[0pt][0pt]{%
\begin{minipage}[c]{2.8in}
\end{minipage} } {%
} \\[1cm]
& Chance & 0.5 & & \\[1cm]

\bottomrule
\end{longtable}

\end{document}


-
Just encase the header word in question, Graph, in its own \multicolumn directive: \multicolumn{1}{c}{Graph}. –  Mico Aug 9 '13 at 10:57
or try \begin{longtable}{ l l l c >{\centering\arraybackslash}m{7cm} } –  Francis Aug 9 '13 at 11:01
you might want to do the same with the header for the last column ("Description"). –  barbara beeton Aug 9 '13 at 12:26
@Mico -- you should post your suggestion as an answer. –  barbara beeton Aug 9 '13 at 12:28

\multicolumn{1}{c}{Graph}