Exponential Growth When a quantity increases by a constant amount per unit time e.g. 1, 3, 5, 7, etc. it is called linear growth. But, when it increases by a fixed percentage it is known as exponential growth e.g. 10, 10 2 , 10 3 , 10 4 ,………….., or 2, 4, 8, 16, 32 etc. Population growth increase in exponential rate and that explains the dramatic increase in global population in the past 150 years. Doubling Time The time needed for a population to double its size at a constant annual rate is known as doubling time. It is calculated as follows: Td = 70/ r where Td = doubling time in years r = annual growth rate If a nation has 2% annual growth rate, its population will double in 35 years. Total Fertility Rate It is one of the key measures of a nation’s population growth. TFR is ...
GEOGRAPHY FOR GEOGRAPHERS