The correct abbreviation for "平方公里" in English is "sq km".
"sq" stands for "square" and "km" stands for "kilometer". This abbreviation is commonly used in various contexts such as measuring land area, population density, or geographical distances. It represents the square of a kilometer, so when you see "sq km", it means the area covered by a kilometer in length and width.
For example, if you say that a particular city has an area of 1000 square kilometers, you would write it as "1000 sq km". This abbreviation helps in expressing large land areas in a concise and standardized manner.
It's important to note that "sq km" is not specific to the metric system and is also used internationally. It is widely understood in scientific research, geographical studies, and everyday discussions when talking about land area measurements.