# The Geometrical Meaning of inner sep in Adjusting the Node Size in TikZ

In the Tikz manual page 53/1318, there is an example to adjust the node size to get a group of circles and squares as below:

The spacing between the two centers of the circles is exactly 1 cm. So what is the geometrical meaning of inner sep=2 mm? In other words which dimension in the resulting figure is 2 mm? Below is the corresponding code:

\documentclass{standalone}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}
[inner sep=2 mm,
place/.style={circle,draw=blue!50,fill=blue!20,thick},
transition/.style={rectangle,draw=black!50,fill=black!20,thick}]
\node at ( 0,2) [place] {};
\node at ( 0,1) [place] {};
\node at ( 0,0) [place] {};
\node at ( 1,1) [transition] {};
\node at (-1,1) [transition] {};
\end{tikzpicture}

\end{document}


The inner sep is the distance from the contents of a node to its border. It is described on page 229 of the manual:

Your nodes have no content, so 2mm is the distance from the node center to the border for the rectangular nodes. For the circular nodes it is from the center to the inscribed rectangle, I believe.

\documentclass{standalone}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}
[inner sep=2 mm,
place/.style={circle,draw=blue!50,fill=blue!20,thick},
transition/.style={rectangle,draw=black!50,fill=black!20,thick}]
\node (a) at ( 0,2) [place] {};
\node at ( 0,1) [place] {};
\node at ( 0,0) [place] {};
\node (b) at ( 1,1) [transition] {};
\node at (-1,1) [transition] {};

\node [draw,minimum size=4mm, densely dotted] at (a.center) {};
\draw [|-|] (a.center) -- ++(2mm,0);
\draw [|-|] (b.center) -- ++(2mm,0);
\end{tikzpicture}

\end{document}