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.
The rood is a unit of area used in historic England with the symbol ro.
Its unit size is equal to 1/4 of an acre, 10,890 ft² or 1,012m². A rectangle equal to one furlong in length and one rod in width is one rood in area.
Its use was very important in surveying land because of the ease of conversion into acres from smaller sections of land.