Where is the discussion of Global Population Distribution Optimization?

Here's an interesting wikipedia overview article on human migration.

http://en.wikipedia.org/wiki/Human_migration

There seems to have been some good expert thought on this topic. But I don't see expert thought on the optimization of global population distribution. Where can I find it?

Most discussion I find are arguments that increasing immigration will lead to "national greatness" for the USA or will ruin the USA or some such thing. How about global migration from the perspective of global welfare? What should we be encouraging? What should we be discouraging? It's weird that optimization of the world economy, trade and even its population are often discussed, but I'm having trouble finding discussion about optimizing the world's population distribution.

I'd guess we'd benefit from a lot more homogenization and megaurbanization (for the benefits of cohesion and economies of scale) but perhaps some populations would benefit from having a large minority or small majority of population with higher social capital mixed in (for example, maybe Lagos would be more optimized if it were 20%-60% Anglo/Han Chinese).