\begin{definition}[Definition:Imperial/Area/Square Mile]
The '''square mile''' is an imperial unit of area.
One '''square mile''' is equal to a square whose side measures $1$ mile.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''square mile'''
}}
{{eqn | r = 640
      | c = acres
}}
{{end-eqn}}
\end{definition}