Make maps tabular

\usepackage{graphicx}
\usepackage{subcaption}

\begin{figure}[htb]
\centering
  \begin{tabular}{@{}cccc@{}}
    \includegraphics[width=.50\textwidth]{map_phys_int_similarity_gini.eps} &
    \includegraphics[width=.50\textwidth]{map_phys_int_perc_local_encounter.eps}  \\
    \includegraphics[width=.50\textwidth]{map_employment_score.eps} &
    \includegraphics[width=.50\textwidth]{map_perc_outgroup_calls_all_day.eps}
  \end{tabular}
  \caption{Maps of Istanbul with measurements
\end{figure}