For humans, population density is the number of people per unit of area, usually quoted per square kilometer or square mile (which may include or exclude, for example, areas of water or glaciers).Commonly this may be calculated for a county, city, country, another territory, or the entire world.f only the Earth's land area of 150 million km 2 (58 million sq. miles) is taken into account, then human population density increases to 47 per km 2 (120 per sq. mile). This includes all continental and island land area, including Antarctica.