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. In many countries, including those in the metric system, square kilometers are the standard unit for land area. For example, the total area of a small country like Luxembourg is about 2,586 square kilometers, illustrating how this measurement helps compare the sizes of different regions.