India: the geographical facets of the world's most populated country

India has become the world's most populated country. It now ranks very highly among the world's economic powerhouses, fourth in nominal GDP and third in GDP in purchasing power parity. The latter per capita has been multiplied eightfold in 30 years. Yet the country still ranks only 125th worldwide. What can a traveller take away from the country in terms of geography, tourism, the economy and culture?