White space creeping in when I place a tikz picture inside another tikz picture

Question

I'm trying to design a seating chart for my classroom. I've done this using pstricks. I wanted to try it in tikz.

What I'm doing is drawing a rectangle to represent each desk. Since the desks are arranged into groups of four, I then group these four rectangles together. The problem I'm having is when I try to group them together, I'm getting unexpected whitespace.

Here's a MWE:

\documentclass{article}
\usepackage[margin=1in,showframe]{geometry}
\setlength{\parindent}{0pt}
\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\mysmallbox}{%%"
  \begin{tikzpicture}
    \node (A) at (0,0) {};
    \node (B) at (6,4) {};
    \draw (A) rectangle (B);
    \draw (A.center|-B.center) -- (A.center-|B.center);
  \end{tikzpicture}}

\newcommand{\boxesInboxes}{%%'
  \begin{tikzpicture}
    \node (A) at (3,2) {\mysmallbox};
    \node (B) at (9,6) {\mysmallbox};
    \draw[color=red,line width=0.1pt] (0,0) rectangle (12,8);
  \end{tikzpicture}}

\pagestyle{empty}
\begin{document}

\mysmallbox

\boxesInboxes

\end{document}

Where is the whitespace coming from?

UPDATE

I found this solution about bounding boxes. That seems far more complicated than I want. Is there a simpler way of pruning the extra white space?

I also found this solution about setting the bounding box, but I still get a little bit of white space in front of the picture.

Answer 1

A node will have inner separation. Make it zero. Further, it is advisable to use coordinates here.

\documentclass{article}
\usepackage[margin=1in,showframe]{geometry}
\setlength{\parindent}{0pt}
\usepackage{tikz}
\usetikzlibrary{calc}

%\newcommand{\mysmallbox}{%%"
%  \begin{tikzpicture}
%    \node (A) at (0,0) {};
%    \node (B) at (6,4) {};
%    \draw (A) rectangle (B);
%    \draw (A.center|-B.center) -- (A.center-|B.center);
%  \end{tikzpicture}}


%% Use coordinate to see the difference
\newcommand{\mysmallbox}{%%
  \begin{tikzpicture}
    \coordinate (A) at (0,0) {};
    \coordinate (B) at (6,4) {};
    \draw (A) rectangle (B);
    \draw (A|-B) -- (A-|B);
  \end{tikzpicture}}

\newcommand{\boxesInboxes}{%%
  \begin{tikzpicture}
    \node[inner sep=0pt] (A) at (3,2) {\mysmallbox};
    \node[inner sep=0pt] (B) at (9,6) {\mysmallbox};
    \draw[color=red,line width=0.1pt] (0,0) rectangle (12,8);
  \end{tikzpicture}}

\pagestyle{empty}
\begin{document}

\mysmallbox

\boxesInboxes

\end{document}