It is not exclusively a population, in India there are currently about one billion and 200 million inhabitants, or of land and climate.
Hinduism, for instance, is not an unitary religion, it’s a term with which we try to encompass practices, customs, beliefs, faiths practiced in India. But in the Hinduist tradition there are also philosophical atheist, devoutly revered deities in certain areas are not even known in other areas.
And then, in addition to the Hindu tradition there are many other religions, not secondary in terms of 'quantity', if you think that India with its 150 million Muslims is the second largest Islamic nation in the world.
In India the feeding varies for different places, people follow multiple calendars and dress in various ways.
Think about the language. Indian law recognizes 18 official languages, but schools teach 50 different languages and movies are produced in 15 languages, while there are newspapers in over 90 languages and radio programs in at least 70 different languages.
And mind you that those aren’t languages similar to each other, some are totally different. Some languages are in fact derived from the Indo-European, such as Sanskrit and Hindi, as other languages have Dravidian source like Tamil and Malayalam, but others are derived from the Mon-Khmer branch and others from Sinotibetano branch.
Malayalam is spoken in Kerala, in Maharashtra Mahara, the Kannada in Karnataka, the Mithila in Bihar, the Konkali in Goa, Hindi is the official language of twelve Indian states, Assam and the Bodo and speaking the Assamese in Andra Pradesh and in Pondhicherry we talk instead Telegu, and then there are the tribal languages like Gondi and Bhil.
The result of all this diversity is that India does not really exist? It does, it does, but as Amartya Sen says in his book The argumentative indian, "the only possible idea of India is that of a nation greater than the sum of its parts."