When some colleagues and I visited India in July, one of the running jokes (Ok, we were tired) centered around where were the 1.1 billion supposed citizens of the country?
I don’t mean that we didn’t see anyone around… everywhere you look in India you see a lot of people. 
It’s just that coming from a part of the world where rural areas have low population densities, it was hard to imagine a different reality. And though India is the 7th largest country in the world, it’s just one third the size of the U.S. (pop. 300 million), and barely bigger than Argentina (pop. 40 million).
A quick off-the-cuff calc gave us this: say India has 20 huge cities, with some 10 million population each, that’s 200 million people. No way were there 900 million people in the rural parts of the country! We just could not fathom it.
[Note: India has 8 out of the 100 largest cities in the world, ranging from 18 million (Mumbai) to 3.5 million (Pune), and totaling 68 million, with an average of 8.5 million. So 20 cities would be 170 million, pretty close to our estimate, eh? 
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Obviously we didn’t actually think that the 1.1 billion figure was untrue, but it was very intriguing to me to know how the people were distributed… So, when I got back home, I got a hold of a very cool global National Geographic map created through "nighttime satellite imagery that provides a snapshot of both population density and energy consumption", to try to understand where those 900 million were hiding. (If you’re wondering, the point of this post is to tell you about these cool maps.
No surprise to see that small European nations were densely populated, and Japan, and the U.S. east coast, but it was astounding (at least to me) to see the high, even distribution across all of India.
Looking at a population density ranking, India is the only large country in the top #100 (they’re #33)! Take a look at persons per square km for the countries we’ve been talking about:
- India: 336
- China: 133
- USA: 30
- Argentina: 13
- Australia: 2
So I’ll finally rest at ease that the Indian Census Bureau is not putting one over on us…
