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Square kilometre (International spelling as used by the International Bureau of Weights and Measures) or square kilometer (American spelling), symbol km2, is a multiple of the square metre, the SI unit of area or surface area.
The are (/ˈɑːr/ or /ˈɛər/) is a unit of area, equal to 100 square metres (10 m × 10 m), used for measuring land area. It was defined by older forms of the metric system, but is now outside of the modern International System of Units (SI).