Physiological population density is a measure of the number of people per unit of area of arable land, which is land that can be used for agriculture.

Crude population density is a measure of the number of people per unit of area of land, which includes both arable land and non-arable land.

Physiological population density is a more accurate measure of the number of people that can be supported by a given area of land.

The world's average physiological population density is 2.5 people per square kilometer of arable land.

The world's average crude population density is 10 people per square kilometer of land.

China has the world's highest physiological population density, at 3.6 people per square kilometer of arable land.

India has the world's second highest physiological population density, at 3.1 people per square kilometer of arable land.

The United States has a physiological population density of 2.7 people per square kilometer of arable land.

The United Kingdom has a physiological population density of 2.4 people per square kilometer of arable land.

Japan has a physiological population density of 2.3 people per square kilometer of arable land.