The square foot is a unit of area and is an imperial unit with the symbol ft².
One square foot is equal in area to a square with edges one foot in length.
It is used a lot in expressing the internal size of a house, apartment, office or other properties so is a useful unit to understand.
The square kilometre is a unit of area and is a multiple of the square metre; an SI derived unit. It has the symbol km².
A square kilometre is equal to the area of a square with edges 1km long. There are 1,000,000 square metres in a square kilometre.
Square kilometres are often used to describe expansive areas of land due to the large unit size.