Spacing issue in table of contents

Question

I'm new here, so I hope I'm adhering to any community rules.

I am trying to create a table of contents for some notes I'd like to record on LaTex. Here is my code:

---

    \documentclass[12pt]{article}

\usepackage[margin=0.90in]{geometry} 
\usepackage{amsmath,amsthm,amssymb,scrextend}
\usepackage{fancyhdr}
\usepackage{titlesec}

\makeatletter
\renewcommand\subsection{\addtocontents{toc}{\protect\addvspace{5\p@}}%
  \if@openright\cleardoublepage\else\clearpage\fi
  \thispagestyle{plain}%
  \global\@topnum\z@
  \@afterindentfalse
  \secdef\@subsection\@ssubsection}
\renewcommand\section{\addtocontents{toc}{\protect\addvspace{20\p@}}%
  \@startsection {section}{1}{\z@}%
  {-3.5ex \@plus -1ex \@minus -.2ex}%
  {2.3ex \@plus.2ex}%
  {\normalfont\Large\bfseries}}
\makeatother


    \begin{document}

% --------------------------------------------------------------
%                         Start here
% --------------------------------------------------------------

\lhead{Physics in Medicine}
\chead{}
\rhead{Revision Notes}

\lfoot{} 
\cfoot{Page \thepage \hspace{1pt} of 16}
\rfoot{}

% \maketitle
\title{\textbf{\textit{Physics in Medicine -- Revision Notes}}}
\date{}

\begin{titlepage}
\vspace{100 mm}
\maketitle
\doublespacing
\tableofcontents
\end{titlepage}
\vfill 

\newpage 

\singlespacing
\addcontentsline{toc}{section}{Section 1: X-ray imaging}
\addcontentsline{toc}{subsection}{What are x-rays?}
\section*{Section 1: X-ray imaging}
\vspace{2mm} 
\newline \noindent \textbf{What are x-rays?}

\vspace{3mm} 

\noindent TEXT

\vspace{10mm}
\addcontentsline{toc}{subsection}{Production of x-rays}

\newline \noindent \textbf{Production of x-rays}
\vspace{8mm}
TEXT

\end{document}

But the result is shown on the picture - horrible big spaces between the content lines. Don't know how to fix this so advice is appreciated :)

Answer 1

The extra space is caused by the redefinition of \section and \subsection. This code contains the line \addtocontents{toc}{\protect\addvspace{20\p@}} (and 5\p@), which adds 20pt and 5pt of vertical space to the table of contents on each use of the \section and subsection commands, respectively.

To remove the extra space, you can remove this part of the redefinition (see MWE below). You can also remove the entire redefinition since it is not necessary, unless you require the additional modifications of the (sub)section title behavior of course.

Some additional space is introduced by \doublespacing (from the setspace package), this can be removed to make the table of contents more compact.

MWE:

\documentclass[12pt]{article}
\usepackage{setspace}

\makeatletter
%\renewcommand\subsection{\addtocontents{toc}{\protect\addvspace{5\p@}}%
\renewcommand\subsection{%
  \if@openright\cleardoublepage\else\clearpage\fi
  \thispagestyle{plain}%
  \global\@topnum\z@
  \@afterindentfalse
  \secdef\@subsection\@ssubsection}
%\renewcommand\section{\addtocontents{toc}{\protect\addvspace{20\p@}}%
\renewcommand\section{%
  \@startsection {section}{1}{\z@}%
  {-3.5ex \@plus -1ex \@minus -.2ex}%
  {2.3ex \@plus.2ex}%
  {\normalfont\Large\bfseries}}
\makeatother

\begin{document}
\title{\textbf{\textit{Physics in Medicine -- Revision Notes}}}
\date{}

\begin{titlepage}
\maketitle
\doublespacing
\tableofcontents
\end{titlepage}

\addcontentsline{toc}{section}{Section 1: X-ray imaging}
\addcontentsline{toc}{subsection}{What are x-rays?}
\section*{Section 1: X-ray imaging}

\addcontentsline{toc}{subsection}{Production of x-rays}

\end{document}

Result: