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 square perch, often referred to as a "square pole" or simply "perch," is an obsolete unit of land area measurement. It was historically used in some English-speaking countries, including the United States and the United Kingdom, for land surveying and property descriptions.
One square perch is equivalent to one square rod or one square pole. In terms of modern measurements, one square perch is approximately equal to 25.29285264 square meters (m²) or 0.00625 acres.
Like other obsolete units of land area measurement, the square perch has largely been replaced by more standardized systems of measurement, such as square meters and square feet, in modern times. It is rarely encountered in contemporary land transactions or legal documents.