Identifying relative location of label

Question

How can I obtain information about the location of a label relative to other text?

• Whether the label is on a previous page or the current page (i.e. appears in some previous lines, but on the same page).
• If the label is on a previous page; how many pages prior? E.g. 1 page before, 5 pages before.

It would be helpful to obtain some value, such as 0 for current page, 1 for the previous page, 2 for two pages previous, as that could be placed into an if-then.

Answer 1

This, perhaps is also a partial answer, since it addresses your first bullet.

The varioref package provides \vref and \vpageref that "decorates" a page reference, depending on its location relative to the reference. Here's an example:

\documentclass{article}
\usepackage{varioref}% http://ctan.org/pkg/varioref
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\begin{document}
\section{First section} \lipsum[1] \label{sec:first} \lipsum[2-3]
\section{Second section} \lipsum[4-5] \label{sec:second} \lipsum[6-8]
\section{Third section} \lipsum[9-12] \label{sec:third} \lipsum[13]
\section{Fourth section} \label{sec:fourth} \lipsum[14]
\section{Last section} \label{sec:last} \lipsum[15-17] \label{doc:end}
See the reference \vpageref{sec:last} or \vpageref{sec:second}.
\end{document}

Answer 2

Here is a partial solution: use \pageref to get the page number of where the \label was defined.

\documentclass{book}
\usepackage{lipsum}

\newcounter{pagedelta}
\newcommand{\pagerefdelta}[1]{%
    \setcounter{pagedelta}{\the\value{page}}%
    \addtocounter{pagedelta}{-\pageref{#1}}%
    \the\value{pagedelta}%
}%

\newcommand{\ShowRef}[1]{Section #1 is on Page~\pageref{#1}\par}%
\begin{document}

\chapter{One}
\section{One-One}\label{One-One}
\lipsum[1-4]\label{One-Two}

\chapter{Two}
\section{Two-One}\label{Two-One}
\section{Two-Two}\label{Two-Two}
\section{Two-Three}\label{Two-Three}

\chapter{Three}
\section{Three-One}\label{Three-One}
\lipsum[1-9]

\newpage
\ShowRef{One-One}
\ShowRef{One-Two}
\ShowRef{Two-One}
\ShowRef{Two-Two}
\ShowRef{Two-Three}
\ShowRef{Three-One}
\end{document}