Because it’s Friday: 7 billion-person ‘continents’

The population of the world has been over 7 billion for about a year now. But those seven billion aren't distributed equally around the globe. 1.2 billion people — about  in India alone (despite it havingjust 2% of the world's land area). At the other end of the spectrum, the entire continent of Australia houses about 0.3% of Australia.

So what would the world look like if we divided it into continents not by political or geographic boundaries, but by population? For the sake of argument, what if the Earth were divided into seven continents of a billion inhabitents each? Armed with MS paint and Wikipedia's table of country populations, Redittor delugetheory drew this map:

Each color on the map represents 1 billion people. The continent of Africa, neatly, already has a total population of around a billion, as do North America and South America combined. (For some reason Greenland and Australia/NZ, with comparatively negligible populations, got thrown in Continent Green as well). For the rest of the world we need some judicious reassembling of the continents. 

While this map was assembled by hand, it would be interesting to see what map an algorithmic approach would create. It would be kind of like a 7-way knapsack problem, I guess. Unfortunately, you couldn't just use country populations as the basis, since China and India already have more than 1 billion inhabitants and need to be split apart. I guess you could arbitrarily break them up into 2 countries each, or perhaps work from the city population list (and distribute the remaining population in countries uniformly over their area). Any R programmers up to the task of automating this problem?