Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world at a time.
Population density:
Population density is the average number of individuals in a population per unit of area or volume.
Population density is calculated as, Population density (D) = Number of people (N)/ Area in km3 (S)
Knowledge of population density is very important for ecological studies of an area.