% siunitx to have the S column specifier,
% which aligns numbers on their decimal point.
\usepackage{siunitx}
\newcommand*{\vcenteredhbox}[1]{\begin{tabular}{@{}c@{}}#1\end{tabular}}
...
\begin{center}
  \vcenteredhbox{\includegraphics[width=0.3\textwidth]{NYC.png}}
  \hspace{0.1\textwidth}
  \begin{minipage}{0.5\textwidth}
    \begin{tabular}{r|S}
      % \multicolumn to remove vertical bar between column headers
      \multicolumn{1}{r}{Borough} &
      % braces to prevent siunitx from misinterpreting the
      % period as a decimal separator
      {Pop. (million)}  \\ \hline
      The Bronx      &1.5  \\
      Brooklyn       &2.6  \\
      Manhattan      &1.6  \\
      Queens         &2.3  \\
      Staten Island  &0.5
    \end{tabular}
  \end{minipage}
\end{center}