Documentation on region.php: You need to include three parameters: region (which can typically take a value of a country, though some larger regions are also allowed), start_date (which is of the form YYYY0000), and end_date (which is of the form YYYY0000). Both start_date and end_date are inclusive. For instance, to get data for India from 1970 to 2010, use /region.php?region=India&start_date=19700000&end_date=20100000.

GDP

Dataset Average Growth (start to end, using linear fit on logarithm)
Graph should be here

GDP per capita

Dataset Average Growth (start to end, using linear fit on logarithm)
Graph should be here

Population

Dataset Average Growth (start to end, using linear fit on logarithm)
Graph should be here