Hectare (ha)
The hectare, or ha, is a metric area unit equal to 10,000 square meters (a square with 100-meter sides). First used in France in 1795, it is now widely used worldwide, particularly in farming, forestry, and land planning. Although it is not an official SI unit, it is permitted because it is practical for measuring fields and properties. Its simple size makes it better than the square kilometer for medium areas.
Square Mile (mi²)
The square mile, or mi², is the area of a square one mile on each side, or 640 acres. Its history dates back to the mile, which originated in Roman times. The square mile became a set measurement in England. It is still widely used in the US and the UK for large areas, such as cities, counties, and parks. Most countries use square kilometers, but in English-speaking regions, the square mile remains common, especially in historical and legal contexts.