A way to measure the distribution of population in a country or region?

The answer is: Population density.

Population density is a useful measure to measure the distribution of population in a country or region. It is calculated by dividing total population by land area, usually expressed as people per square kilometre. This measure is often used to compare population density between different countries or regions and to identify areas with high and low population density. It can also provide insight into how population growth affects the environment, economy, and quality of life in a particular area. By understanding population density, governments and citizens can better plan for the future and make informed decisions.