A square kilometer is a unit of area measurement that is equal to a square with each side measuring one kilometer long. It is commonly used to measure large land areas, such as cities, parks, and countries. One square kilometer is equivalent to 1,000,000 square meters, making it a useful unit for understanding the size of geographical spaces. This measurement is often used in various fields, including urban planning, environmental studies, and agriculture. For example, the area of a city like Tokyo or a national park like Yellowstone can be expressed in square kilometers to provide a clear understanding of their size and scale.