How can I change the whitespace above and below center?

Question

Is it possible to control the space above and below center, e.g. the way it can be controlled above and below math display? In other words, is there an equivalent to, say,

\setlength\abovedisplayskip{3pt plus 2pt minus 2pt}
\setlength\belowdisplayskip{3pt plus 2pt minus 2pt}

Answer 1

The center environment is actually defined in terms of a list, so you can tweak all the parameters detailed in Section 56 of source2e.

In terms of the spacing above the center environment, you can use something like

\documentclass{article}
\usepackage{lipsum}
\let\oldcenter\center
\let\oldendcenter\endcenter
\renewenvironment{center}{\setlength\topsep{0pt}\oldcenter}{\oldendcenter}
\begin{document}

\lipsum[1]
\begin{center}
    \lipsum[2]
\end{center}

\end{document}

The spacing below could be controlled by adding some glue at the end of the environment (after \oldendcenter).

Answer 2

You can define your mycenter environment and pass a length (optionally) to modify the top/bottom gap:

\documentclass{article}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage[margin=1in]{geometry}% http://ctan.org/pkg/geometry
\newenvironment{mycenter}[1][\topsep]
  {\setlength{\topsep}{#1}\par\kern\topsep\centering}% \begin{mycenter}[<len>]
  {\par\kern\topsep}% \end{mycenter}
\setlength{\parindent}{0pt}% Just for this MWE
\begin{document}
1: \lipsum[2]
\begin{center}
  2: \lipsum[2]
\end{center}
3: \lipsum[2]
\begin{mycenter}
  4: \lipsum[2]
\end{mycenter}
5: \lipsum[2]
\begin{mycenter}[0pt]
  6: \lipsum[2]
\end{mycenter}
7: \lipsum[2]
\end{document}

geometry and lipsum were loaded specifically for this MWE, and may not be needed in your final document.