How to horizontally and vertically align a matrix of subfloats?

Question

Assume you have a matrix of 2x2 tikz figures and you decide to use subfloats. The code

\documentclass{report}

\usepackage{subfig}
\usepackage{tikz}

\begin{document}

\begin{figure}[ht!]
    \center
    \subfloat[Figure 1]{
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (1,1);
        \end{tikzpicture}   
    } \quad
    \subfloat[Figure 2]{
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (3,3);
        \end{tikzpicture}   
    } \\
    \subfloat[Figure 3]{
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (2,2);
        \end{tikzpicture}   
    } \quad
    \subfloat[Figure 4]{
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (5,5);
        \end{tikzpicture}   
    }
    \caption{Test}
    \label{test}
\end{figure}

\end{document}

gives the result

How can one now obtain a symmetric alignment in both lines and columns, as shown below? I suppose this is a standard question and should have a simple solution, but so far I've only found methods such as

• Using a tabular (see here)
• Using valign with includegraphics (see here) but I am using tikzpictures.
• Using minipage (see here)
• ...

Answer 1

With use of tabularx for positioning of images and their captions:

\documentclass{report}
\usepackage[skip=1ex]{caption}
\usepackage{tabularx}
\newcolumntype{C}[1]{>{\centering\arraybackslash\hsize=#1\hsize}X}
\usepackage{tikz}

\begin{document}

\begin{figure}[htp!]
    \centering
\renewcommand\tabularxcolumn[1]{m{#1}}
    \begin{tabularx}{0.8\linewidth}{C{0.8}C{1.2}}
\tikz\filldraw (0,0) rectangle (1,1);
    &   \tikz\filldraw (0,0) rectangle (3,3);   \\  
\caption{Figure 1}
    &   \caption{Figure 2}  \\
\tikz\filldraw (0,0) rectangle (2,2);
    &   \tikz\filldraw (0,0) rectangle (5,5);   \\  
\caption{Figure 3}
    &   \caption{Figure 4}  \\[-2ex]
\end{tabularx}

\caption{Test}
\label{test}
    \end{figure}
\end{document}

Answer 2

Probably not the most elegant code, but the following should result in an output close to the expected one.

\documentclass{report}
\usepackage{subcaption}
\usepackage{tikz}

\begin{document}

\begin{figure}[ht!]
\centering
    \begin{subfigure}{0.2\textwidth}
      \centering
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (1,1);
        \end{tikzpicture}   
    \end{subfigure}\quad
    \begin{subfigure}{0.45\textwidth}
      \centering
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (3,3);
        \end{tikzpicture}  
    \end{subfigure}
    \smallskip
    
    \begin{subfigure}{0.2\textwidth}
        \caption{Figure 1} 
    \end{subfigure}\quad
    \begin{subfigure}{0.45\textwidth}
        \caption{Figure 2} 
    \end{subfigure}
    
    \bigskip
    \begin{subfigure}{0.2\textwidth}
      \centering
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (2,2);
        \end{tikzpicture}  
    \end{subfigure}\quad
    \begin{subfigure}{0.45\textwidth}
      \centering
        \begin{tikzpicture}
        \filldraw (0,0) rectangle (5,5);
        \end{tikzpicture}  
    \end{subfigure} 
    \smallskip
    
    \begin{subfigure}{0.2\textwidth}
        \caption{Figure 3} 
    \end{subfigure}\quad
    \begin{subfigure}{0.45\textwidth}
        \caption{Figure 4} 
    \end{subfigure} 
    \caption{Test}
    \label{test}
\end{figure}

\end{document}

Answer 3

If you don't have too many of these structures, you can cheat.

\documentclass{report}

\usepackage{subfig}
\usepackage{tikz}

\begin{document}

\begin{figure}[htp!]
\centering

\begin{tabular}{cc}
  \begin{tabular}{@{}c@{}}
  \begin{tikzpicture}
  \filldraw (0,0) rectangle (1,1);
  \end{tikzpicture}
  \end{tabular}
&
  \begin{tabular}{@{}c@{}}
  \begin{tikzpicture}
  \filldraw (0,0) rectangle (3,3);
  \end{tikzpicture}
  \end{tabular}
\\[-2ex]
  \subfloat[Figure 1]{\hspace{3cm}}
&
  \subfloat[Figure 2]{\hspace{3cm}}
\\[6ex]
  \begin{tabular}{@{}c@{}}
  \begin{tikzpicture}
  \filldraw (0,0) rectangle (2,2);
  \end{tikzpicture}
  \end{tabular}
&
  \begin{tabular}{@{}c@{}}
  \begin{tikzpicture}
  \filldraw (0,0) rectangle (5,5);
  \end{tikzpicture}
  \end{tabular}
\\[-2ex]
  \subfloat[Figure 3]{\hspace{3cm}}
&
  \subfloat[Figure 4]{\hspace{3cm}}
\end{tabular}

\caption{Test}
\label{test}

\end{figure}

\end{document}