The square mile is a unit of area and is an imperial unit with the symbol mi².
One square mile is equal in area to a square with edges one mile in length.
The Romans established the square mile; computed through a system of feet, paces and marches. The square mile's existence still remains in some places; for example "The Square Mile" is a term often used to describe the very centre of London in the UK (which just so happens to measure 1mi²).
The square centimetre is a unit of area and is a multiple of the square metre; an SI derived unit. It has the symbol cm².
A square centimetre is equal to the area of a square with edges 1cm long. There are 10,000 square centimetres in a square metre.
It is often used to describe areas smaller than 1m² - including much work in classrooms on paper.