A country’s geographic often has little bearing on its population, as shown by this world map adjusted for population size.
See a larger version here.
Some of the results may be surprising: Bangladesh, which is about the size of Iowa, has more people than Russia, which is nearly twice as big as the U.S. That little green blip above China is Mongolia, which is bigger than Western Europe but has fewer people than South Florida.
Countries like Nigeria, Ethiopia, Vietnam, and Indonesia are far larger than most people realize. This is part of the reason the economic power and wealth is accruing to the developing world: their young and growing populations, if properly governed and invested in, offers considerable economic potential.