Population growth 

- it refers to an increase in the World's population over time.

-Population explosion refers to a sudden and increase in a countries population.

-an increase in the population can take place for two reason:

1. Natural increase- refers to the number of births (birth rate or fertility rate) exceeding the number of deaths (death rate or mortality) in a region.

2. Migration- refers to the movement of people across the globe. When people move into a region, we call this immigration and when people out of a region, we refer to this as emigration.

The demographic Transition Model

-in every country there is need to move from high birth and death rates to low birth and death rates.

-the move is called transition and such chnages are clearly indicated graphically in a demographic tranisition model.