Which of the following best defines population density?

Population density is defined as the average number of people living per unit area, typically expressed in terms such as people per square kilometer or square mile. This measure gives insight into how crowded or sparsely populated an area is and can help understand various socio-economic factors, resource distribution, and urban planning.

In relation to the other options, while "all individuals of a species in an area" refers to a concept relevant to ecology and biodiversity rather than human populations, the "growth rate of a population" pertains to the increase or decrease in numbers over time but does not reflect the spatial aspect of population distribution. Lastly, the "impacts of natural disasters" involve the consequences that these events have on communities, but again, this concept does not define population density itself. Therefore, the focus on the average number of people per unit area effectively captures the idea of population density.