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  Open an example of cross-referencing figures in Overleaf

In LaTeX, we can label entities that are numbered (sections, formulas, etc), and then use that label to refer to them elsewhere, and the same commands apply to the figure environment as well (they are numbered).

Basics of Labels and Referencing

\label{marker}

The marker can be seen as a name that we give to the object that we want to reference. It's important to add \label after a numbered element e.g. \section, \subsection, \caption etc, otherwise the label won't "latch on" to the correct number or counter.

\ref{marker}

This prints the number assigned to the object labeled by marker.

\pageref{marker}

This prints the number of the page where the object labeled by marker appears.

Compiling a LaTeX document with labels and references

The marker used to label objects is not shown anywhere in the document, and references to it are replaced with the appropriate numbers. If we reference a non-existent marker, LaTeX will compile successfully but with a warning about undefined references. The reference to the unknown marker will be replaced by ??.

In the example from Overleaf included above, you can see that we could successfully add reference to figures included in the document later. To make it possible, LaTeX has to be run twice - the first run compiles and stores all labels and their positions, and in the second run all the references are replaced with the appropriate numbers. Thus, we have to compile our document twice to see the correct output.

Using meaningful names to refer to figures

Since we can use any string as a label, it's a common practice to add a few letters to the label (as prefix) to indicate what is being labeled. This becomes important when a lot of different types of objects are referenced in a document, as it might be useful to remember the kind of object a label refers to it. Besides, it also makes it possible to reference different kind of objects using a common string.

For example, if a document contains

  • a section on population of nations,
  • a table containing the population numbers, and
  • a figure containing a bar chart of the population sizes,

it might be convenient to refer to all of them using variants of population. This can be accomplished by using the labels

  • sec:population for the section,
  • tab:population for the table, and
  • fig:population for the figure.

The following is an example for figures -

\begin{figure}[h!]
  \includegraphics[scale=1.7]{birds.jpg}
  \caption{The birds}
  \label{fig:birds}
\end{figure}

Again, note that \label is given after \caption.

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