Let's cut to the chase: the Milky Way galaxy is a vast, flat, disk-shaped collection of gas, dust, and stars — a sprawling megalopolis that's a mind-crushing 100,000 light years across and several thousand light years thick.
Experts say the stretch of West Africa's coastline from Abidjan to Lagos is on track to become the world's largest megalopolis, and could be home to half a billion people by the end of this century.