I'm not suggesting densely packing the population into cities.  I'd advocate for the opposite.  We live in the digital age, and many of us do work that could be done from anywhere that has access to water, electric power, and internet access.  Bring the infrastructure to where the people already are, in the most cost-effective means available in the third world: coal fired power plants.  It takes steel to build water treatment plants and pipelines, and it takes coal to make steel.