why this KvMap is not centered?

Question

I have this K-Map written with the KvMap package, but I don't know how to center it properly:

\documentclass[a4paper,12pt]{article}
\usepackage[a4paper, margin=2cm]{geometry}
\usepackage[utf8]{inputenc}

\usepackage{kvmap}
\usetikzlibrary{backgrounds}

\begin{document}
    \begin{center}
        \begin{kvmap}
          \kvlist{8}{4}{\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},\phantom{0},X,X,X,X,X,X,X,X,\phantom{0},1,1,\phantom{0},X,X,X,\phantom{0}}{Q_2, Q_1, Q_0 ,Q_4 ,  Q_3 }
          \foreach \tikzn/\tikzi in {00/0, 10/1, 20/3, 30/2, 40/6, 50/7, 60/5, 70/4,
            01/8, 11/9, 21/11, 31/10, 41/14, 51/15, 61/13, 71/12,
            02/24, 12/25, 22/27, 32/26, 42/30, 52/31, 62/29, 72/28,
            03/16, 13/17, 23/19, 33/18, 43/22, 53/23, 63/21, 73/20
          } 
          {\node[font=\footnotesize,anchor=north east, inner sep=0.25pt] at (\tikzn.north east) {$\tikzi$};}
          \begin{scope}[on background layer]
            \fill[gray!30] (1,-2) rectangle (3,-4);
            \fill[gray!30] (5,-2) rectangle (7,-4);
          \end{scope}
        \end{kvmap}
    \end{center}
\end{document}

I would like to have the same space from the left and right side of the Kmap.

Answer 1

The kvmap is centered. However, you're right into thinking that it doesn't appear centered, because the eye is led by the vertical rules.

You can tell TeX to back up the width of the label Q₄Q₃ by inserting a negative space.

\documentclass[a4paper,12pt]{article}
\usepackage[a4paper, margin=2cm]{geometry}
\usepackage[utf8]{inputenc}

\usepackage{calc}
\usepackage{kvmap}
\usetikzlibrary{backgrounds}

\usepackage{showframe} % just to show the margins, remove it

\begin{document}

\begin{center}

\settowidth{\dimen0}{$Q_4Q_3$}\hspace*{-\dimen0}%
\begin{kvmap}
  \kvlist{8}{4}{\phantom{0},\phantom{0},\phantom{0},\phantom{0},
                \phantom{0},\phantom{0},\phantom{0},\phantom{0},
                \phantom{0},\phantom{0},\phantom{0},\phantom{0},
                \phantom{0},\phantom{0},\phantom{0},\phantom{0},
                X,X,X,X,X,X,X,X,\phantom{0},1,1,\phantom{0},X,X,X,
                \phantom{0}}
               {Q_2, Q_1, Q_0, Q_4, Q_3}
  \foreach \tikzn/\tikzi in {
    00/0, 10/1, 20/3, 30/2, 40/6, 50/7, 60/5, 70/4,
    01/8, 11/9, 21/11, 31/10, 41/14, 51/15, 61/13, 71/12,
    02/24, 12/25, 22/27, 32/26, 42/30, 52/31, 62/29, 72/28,
    03/16, 13/17, 23/19, 33/18, 43/22, 53/23, 63/21, 73/20
  } 
  {
   \node[font=\footnotesize,anchor=north east, inner sep=0.25pt] at (\tikzn.north east) {$\tikzi$};
  }
  \begin{scope}[on background layer]
    \fill[gray!30] (1,-2) rectangle (3,-4);
    \fill[gray!30] (5,-2) rectangle (7,-4);
  \end{scope}
\end{kvmap}

\end{center}
\end{document}