The phrase "per square km" is correct and commonly used in written English.
It is typically used to express a measurement of something in relation to a specific unit of area (in this case, square kilometers). Example: The population density of the city is 1,000 people per square km.
There are five beekeepers for every thousand people, and eight hives per square km (in the UK, it's just one).
By comparison, omnivorous mammals average about 8 per square km (20 per square mile), and herbivorous rodents attain densities of up to 40,000 per square km (100,000 per square mile) at peak population.
The population, averaging only 2.3 persons per square mile (0.9 per square km), consists chiefly of Russian settlers.
As wetlands are among the most productive habitats, they can support as many as 55 sitatungas per square km (142 sitatungas per square mile).
The extremely high overall population density of Bangladesh, averaging more than 2,500 persons per square mile (1,000 per square km) in the early 21st century, varies widely according to the distribution of flatland.
The island averages more than 2,600 persons per square mile (1,000 per square km) and has the majority of Indonesia's population on only 7 percent of the total land area of the republic.
In this study, the levels of urbanization were categorized into 3 groups, urban (above ten thousand), suburban (ranged one thousand to below ten thousand), and rural (below one thousand) based on density of the population (person per square kilometer, km).
Tanzania is sparsely populated with average population density of 51 inhabitants per square kilometre (inh./sq. km) with interregional and urban rural significant variations (NBS and Office of Chief Stastitian Zanzibar 2013).
In general, carnivores have a population density of approximately 1 per 2.5 square km (1 per square mile).
Assuming a yam patch density of 0.4 (=10.7/28) per square kilometer, a forest of 320 km would contain 96 patches, which meets the requirements of the annual 6-month-long molongo for 50 people.
More specifically, it refers to the measure of the frequency of earthquakes in a region for example, the number of earthquakes of magnitude between 5 and 6 per 100 square km (39 square miles).
