<Ul> <Li> Increased problems with locating sexual mates </Li> <Li> Increased inbreeding </Li> </Ul> <Li> Increased problems with locating sexual mates </Li> <P> 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 . </P> <P> The world's population is around 7,500,000,000 and Earth's total area (including land and water) is 510,000,000 square kilometers (197,000,000 sq. mi .). Therefore, the worldwide human population density is around 7,500,000,000 ÷ 510,000,000 = 14.7 per km (38 per sq. mi). If only the Earth's land area of 150,000,000 km (58,000,000 sq. mi .) is taken into account, then human population density increases to 50 per km (129 per sq. mile). This includes all continental and island land area, including Antarctica . If Antarctica is also excluded, then population density rises to over 55 people per km (over 142 per sq. mile). However, over half of the Earth's land mass consists of areas inhospitable to human habitation, such as deserts and high mountains, and population tends to cluster around seaports and fresh - water sources . Thus, this number by itself does not give any helpful measurement of human population density . </P>

The number of persons per square kilometer in a country is called