A square hectometer (often abbreviated as hm²) is a unit of area in the International System of Units (SI). It represents a square with sides that each measure 100 meters (10,000 centimeters) in length.
One square hectometer is equal to 10,000 square meters (m²) because each side of the square is 100 meters long, and when you square that length, you get 10,000 square meters.
To put it in perspective, a square hectometer is equivalent to 0.01 square kilometers (km²) because 1 square kilometer is equal to 100 hectares.
Square hectometers are not as commonly used as some other units of area, but they can be helpful for measuring large land areas, especially in some scientific and land management contexts.
A rood is an old and largely obsolete unit of land area measurement. It was historically used in some English-speaking countries, particularly in the United Kingdom and Ireland, but it is not commonly used today, and its use in official measurements has been largely phased out.
In the traditional system, one rood is equal to one-quarter of an acre. This means that there are 4 roods in one acre. Converting to modern units, one rood is approximately 1,011.71 square meters (m²) or 0.101171 hectares (ha).
The term "rood" is often associated with medieval land measurement systems and was used in land and property transactions in the past. While it may occasionally appear in historical documents or literature, it is no longer a standard unit of measurement for land area in most countries.