Tikzmark Annotations Overlapping with Footer

Question

Currently, my tikzmark annotations overlap with my footer defined by the fancyhdr package.

Currently I have my equation with the annotation defined like

\begin{equation}
\tikzmarknode{A}{2}
\end{equation}
\begin{tikzpicture}[overlay,remember picture, shorten <= 1mm, font=\footnotesize]
\draw[red,<-] (A.south) -- ++ (-0.3,-1) node[below] {2 spin states};
\end{tikzpicture}

I presume I have to put the equation and the tikzmark annotation in the same box so LaTeX knows to put the entire box on the next page. What's the proper way to do this?

EDIT: My equation looks something more like this

\begin{equation}
    \tikzmarknode{A}{2}\left[\frac{\tikzmarknode{B}{(2k_{F})}}{\tikzmarknode{C}{\left(\frac{2\pi}{Na}\right)}}\right]=\tikzmarknode{D}{n}\tikzmarknode{E}{(Na)}
\end{equation}
\begin{tikzpicture}[overlay,remember picture,shorten <=1mm,font=\footnotesize]
    \draw[red,<-] (A.south) -- ++ (-0.3,-0.3) node[left,xshift=0.1cm,yshift=-0.1cm] {2 spin states};
    \draw[red,<-] (B.east) -- ++ (1,0.6) node[right] {volume of Fermi sea};
    \draw[red,<-] (C.south) -- ++ (0.2,-0.4) node[below right,xshift=-0.1cm,yshift=0.2cm] {volume corresponding to a single $k$ since $k$ is quantized as $k=\frac{2\pi m}{Na}$, $m\in\mathbb{Z}$};
    \draw[red,<-] (D.south) -- ++ (0.3,-0.3) node[right,xshift=-0.1cm,yshift=-0.1cm] {number density};
    \draw[red,<-] (E.east) -- ++(0.8,0.2) node[right] {length of chain};
\end{tikzpicture}

Answer 1

You can measure the dimensions of the annotations and add the corresponding space in the equation. It is still less automatic than one may wish.

\documentclass[fleqn]{article}
\usepackage{amssymb}
\usepackage{lipsum}
\usepackage{tikz}
\usetikzlibrary{tikzmark,calc}
\begin{document}
\lipsum[1]
\begin{equation}
    \tikzmarknode{A}{2}\left[\frac{\tikzmarknode{B}{(2k_\mathrm{F})}}{\tikzmarknode{C}{\left(\frac{2\pi}{Na}\right)}}\right]=\tikzmarknode{D}{n}\tikzmarknode{E}{(Na)}
\begin{tikzpicture}[overlay,remember picture,shorten <=1mm,font=\footnotesize]
  \begin{scope}[local bounding box=annotations]
    \draw[red,<-] (A.south) -- ++ (-0.3,-0.3) node[left,xshift=0.1cm,yshift=-0.1cm] {2 spin states};
    \draw[red,<-] (B.east) -- ++ (1,0.6) node[right] {volume of Fermi sea};
    \draw[red,<-] (C.south) -- ++ (0.2,-0.4) node[below right,xshift=-0.1cm,yshift=0.2cm] {volume corresponding to a single $k$ since $k$ is quantized as $k=\frac{2\pi m}{Na}$, $m\in\mathbb{Z}$};
    \draw[red,<-] (D.south) -- ++ (0.3,-0.3) node[right,xshift=-0.1cm,yshift=-0.1cm] {number density};
    \draw[red,<-] (E.east) -- ++(0.8,0.2) node[right] {length of chain};
  \end{scope}
    \path let \p1=($(annotations.north)-(annotations.south)$),
  \p2=($(annotations.center)-(A.center)$),\n1={\y1-\baselineskip} in 
   \pgfextra{\xdef\myht{\n1}\xdef\mylift{\y2}};
\end{tikzpicture}
  \raisebox{\mylift}{$\begin{array}{@{}c@{}}\vspace{\myht}\end{array}$}
  \typeout{\myht}
\end{equation}
\lipsum[2]
\end{document}

Answer 2

tikzmark may overlap anything on a page by itself meaning and motivation. To avoid overlapping, you can manually add a \vspace{8mm} (and followed by a blank line), for example.

\documentclass{article}
\usepackage{tikz,lipsum}
\usetikzlibrary{tikzmark}
\begin{document}
\lipsum[1]
\begin{equation}
\tikzmarknode{A}{2}=1+1
\end{equation}
\begin{tikzpicture}[overlay,remember picture, shorten <= 1mm, font=\footnotesize]
\draw[red,<-] (A.south) -- ++ (-0.3,-1) node[below] {2 spin states};
\end{tikzpicture}
\vspace*{8mm}

\lipsum[1]
\end{document}