Question

Whst is a plain? Why is it thickly populated

Answer 1

Plain is a geographical area which is has no bumpy surface
It is thickly population Due to its fertility and easy availability of resources

Answer 2

 A plain is a flat area which is not much high in elevation which occurs between two highlands like between two plateaus or mountains.these areas are highly fertile as the rivers that descend from the mountains deposit its rich silt in these areas making it highly productive area.these ares are very good for agriculture.and most of the plains are thickly populated because of the availability of  good transport system