How to label/tag TikZ diagrams?

Question

I would like to be create diagrams using TikZ that have a number on the side of the page (like the equation environment makes) that I can label using \label and cross-reference using \ref.

Essentially, I am looking for something like \tag that works inside the tikzpicture environment.

For a concrete example, I would like to create something like the first two diagrams on the following page.

Does anyone know how this can be done in TikZ specifically?

Answer 1

You can put everything you like into the equation environment. Like this, it will behave like an equation which seems to be what you want.

% arara: pdflatex

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{blindtext}

\begin{document} 
\setcounter{page}{15}
\noindent
into a commutative diagramm 
\begin{equation}
    \begin{tikzcd}
        B\times_A C \arrow{r}{\pi_2}\arrow{d}[swap]{\pi_1} & C\arrow{d}{g} \\
        B \arrow{r}[swap]{f} & A;
    \end{tikzcd}
\end{equation}
\blindtext

In a general category $C$, one says that a commutative square
\begin{equation}
    \begin{tikzcd}
        P \arrow{r}{q}\arrow{d}[swap]{p} & C\arrow{d}{g} \\
        B \arrow{r}[swap]{f} & A
    \end{tikzcd}
\end{equation}
\blindtext
\end{document} 

---

If you which to have the last diagram as well:

\begin{equation*}
    \begin{tikzcd}
        X\arrow{drr}{\gamma}\arrow[dashed]{dr}[near end]{!\delta}\arrow{ddr}[swap]{\beta} & & \\[1ex]
        & P \arrow{r}{q}\arrow{d}[swap]{p} & C\arrow{d}{g} \\
        & B \arrow{r}[swap]{f} & A
\end{tikzcd}
\end{equation*}